Quantum dots, a composition or composite including the same, and an electronic device including the same

ABSTRACT

A quantum dot including a core including a quaternary alloy semiconductor nanocrystal and not including cadmium, a composition and a quantum dot polymer composite including the same, and an electronic device including the same. 
     The quaternary alloy semiconductor nanocrystal comprises indium (In), phosphorous (P), zinc (Zn), and selenium (Se), and in the core, a ratio of the zinc with respect to the indium is less than or equal to about 0.5:1 and in the core, a ratio of selenium with respect to zinc is less than or equal to about 0.6:1.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of application Ser. No.16/431,772, filed Jun. 5, 2019, which claims priority to and the benefitof Korean Patent Application No. 10-2018-0065098, filed in the KoreanIntellectual Property Office on Jun. 5, 2018, and all the benefitsaccruing therefrom under 35 U.S.C. § 119, the content of which isincorporated herein in its entirety by reference.

BACKGROUND 1. Field

Quantum dots, a composition or composite including same, and anelectronic device including the same are disclosed.

2. Description of the Related Art

Unlike a bulk material, quantum dots (e.g., nano-sized semiconductornanocrystals) may have different energy bandgaps by controlling thesizes and compositions of the quantum dots. Quantum dots may exhibitelectroluminescent and photoluminescent properties. In a colloidalsynthesis, organic materials such as a dispersing agent may coordinate,e.g., be bound, to a surface of the semiconductor nanocrystal during thecrystal growth thereof, thereby providing a quantum dot having acontrolled size and having luminescent properties. From an environmentalstandpoint, developing a cadmium free quantum dot with improvedluminescent properties is desirable.

SUMMARY

An embodiment provides cadmium free quantum dots that may exhibitimproved photoluminescence properties and enhanced stability.

An embodiment provides a method of producing the cadmium free quantumdots.

An embodiment provides a composition including the cadmium free quantumdot.

An embodiment provides a quantum dot-polymer composite including cadmiumfree quantum dot.

An embodiment provides a layered structure and an electronic deviceincluding the quantum dot-polymer composite.

In an embodiment, a quantum dot includes a core including a quaternaryalloy semiconductor nanocrystal, wherein the quantum dot does notinclude cadmium, wherein the quaternary alloy semiconductor nanocrystalincludes indium (In), phosphorous (P), zinc (Zn), and selenium (Se), andin the core, a mole ratio of the zinc with respect to the indium is lessthan or equal to about 0.5:1 and in the core, a mole ratio of seleniumwith respect to zinc is less than or equal to about 0.6:1.

In the core, the mole ratio of zinc with respect to indium may be lessthan or equal to about 0.45:1 and in the core, and the mole ratio ofselenium with respect to zinc may be less than or equal to about 0.51:1.

The core may have a first absorption peak wavelength of less than orequal to about 460 nanometers (nm) in an ultraviolet-visible (UV-Vis)absorption spectrum of the core.

The quaternary alloy semiconductor nanocrystal may include a homogeneousalloy.

The core may have a size of greater than or equal to about 2 nm and lessthan or equal to about 3 nm.

In the core, a mole ratio of a total sum of the zinc and the seleniumwith respect to a total sum of the indium and the phosphorous may begreater than or equal to about 0.2:1, or greater than or equal to about0.3:1 and less than or equal to about 0.65:1, or less than or equal toabout 0.5:1.

The quantum dot may have a semiconductor nanocrystal shell on (e.g.,directly on) the core and the semiconductor nanocrystal shell mayinclude zinc, selenium, and sulfur.

The semiconductor nanocrystal shell may include a first layer disposeddirectly on the core and a second layer disposed on the first layer, thefirst layer including a first semiconductor nanocrystal, and the secondlayer including a second semiconductor nanocrystal having a compositiondifferent from a composition of the first semiconductor nanocrystal.

An energy bandgap of the second semiconductor nanocrystal may be greaterthan or equal to an energy bandgap of the first semiconductornanocrystal.

The first semiconductor nanocrystal may include zinc, selenium, andoptionally sulfur.

The second semiconductor nanocrystal may include zinc and sulfur. Thesecond semiconductor nanocrystal may not include selenium.

A thickness of the first layer may be greater than or equal to about 3monolayers.

A thickness of the first layer may be less than or equal to about 10monolayers.

The second layer may be an outermost layer of the quantum dot.

A thickness of the second layer may be greater than or equal to about 1monolayer.

A thickness of the second layer may be less than or equal to about 10monolayers.

A maximum photoluminescence peak of the quantum dot may be in a range offrom about 500 nm to about 580 nm.

A maximum photoluminescence peak of the quantum dot may have a fullwidth at half maximum of less than or equal to about 45 nm.

A quantum efficiency of the quantum dot may be greater than or equal toabout 70%.

In an embodiment, a method of producing the quantum dot includes:

-   -   preparing a reaction liquid including an organic ligand, an        indium precursor, a zinc precursor, a selenium precursor, and a        phosphorous precursor in an organic solvent; and conducting a        reaction in the reaction liquid at a temperature of about        greater than or equal to about 290° C. for a time period of less        than or equal to about 1 hour to obtain a core including a        quaternary alloy semiconductor nanocrystal (hereinafter, also        referred to as an alloy core) and produce the quantum dot.

Preparing the reaction liquid may include mixing the indium precursorand the zinc precursor in the organic solvent in the presence of theorganic ligand to obtain a mixture; heating the mixture at a temperatureof about 150° C. and 220° C. to obtain a heated mixture; and adding theselenium precursor and the phosphorous precursor to the heated mixture.

The reaction liquid may not include an alkyl thiol.

The method may further include forming a semiconductor nanocrystal shellon the alloy core.

In an embodiment, a composition includes the aforementioned quantum dot,a dispersing agent (e.g., a carboxylic acid group containing binderpolymer), a photopolymerizable monomer including a carbon-carbon doublebond, a photoinitiator, and a solvent (e.g., an organic solvent).

The binder polymer may include a carboxylic acid group containing binderpolymer, which includes:

a copolymer of a monomer mixture including a first monomer including acarboxylic acid group and a carbon-carbon double bond, a second monomerincluding a carbon-carbon double bond and a hydrophobic moiety and notincluding a carboxylic acid group, and optionally a third monomerincluding a carbon-carbon double bond and a hydrophilic moiety and notincluding a carboxylic acid group;

a multiple aromatic ring-containing polymer having a backbone structurein which two aromatic rings are bound to a quaternary carbon atom thatis a constituent atom of another cyclic moiety in a main chain of thebackbone structure, the multiple aromatic ring-containing polymerincluding a carboxylic acid group (—COOH);

or a combination thereof.

The carboxylic acid containing binder polymer may have an acid value ofgreater than or equal to about 50 milligrams of potassium hydroxide(KOH) per gram (mg KOH/g) and less than or equal to about 240 mg KOH/g.

The composition may further include a (multiple or mono-functional)thiol compound including a thiol group at a terminal end of the thiolcompound, a metal oxide particulate, or a combination thereof.

When a plurality of metal oxide particles is present, the plurality ofmetal oxide particles may include TiO₂, SiO₂, BaTiO₃, Ba₂TiO₄, ZnO, or acombination thereof.

The thiol compound may include a compound represented by ChemicalFormula 1:

wherein,

R¹ is hydrogen; a substituted or unsubstituted C1 to C30 linear orbranched alkyl group; a substituted or unsubstituted C6 to C30 arylgroup; a substituted or unsubstituted C3 to C30 heteroaryl group; asubstituted or unsubstituted C3 to C30 cycloalkyl group; a substitutedor unsubstituted C3 to C30 heterocycloalkyl group; a C1 to C10 alkoxygroup; a hydroxy group; —NH₂; a substituted or unsubstituted C1 to C30amine group, wherein —NRR′, wherein R and R′ are independently hydrogenor C1 to C30 linear or branched alkyl group, but simultaneously nothydrogen; an isocyanate group; a halogen; —ROR′, wherein R is asubstituted or unsubstituted C1 to C20 alkylene group and R′ is hydrogenor a C1 to C20 linear or branched alkyl group; an acyl halide, wherein—RC(═O)X, wherein R is a substituted or unsubstituted alkylene group andX is a halogen; —C(═O)OR′, wherein R′ is hydrogen or a C1 to C20 linearor branched alkyl group; —CN; —C(═O)NRR′, wherein R and R′ areindependently hydrogen or a C1 to C20 linear or branched alkyl group;—C(═O)ONRR′, wherein R and R′ are independently hydrogen or a C1 to C20linear or branched alkyl group; or a combination thereof,

L₁ is a carbon atom, a substituted or unsubstituted C1 to C30 alkylenegroup, a substituted or unsubstituted C1 to C30 alkylene group wherein amethylene (—CH₂—) is replaced by a sulfonyl (—SO₂—) moiety, a carbonyl(CO) moiety, an ether (—O—) moiety, a sulfide (—S—) moiety, a sulfoxide(—SO—) moiety, an ester (—C(═O)O—) moiety, an amide (—C(═O)NR—) moiety(wherein R is hydrogen or a C1 to C10 alkyl group), or a combinationthereof, a substituted or unsubstituted C3 to C30 cycloalkylene group, asubstituted or unsubstituted C6 to C30 arylene group, a substituted orunsubstituted C3 to C30 heteroarylene group, or a substituted orunsubstituted C3 to C30 heterocycloalkylene group,

Y₁ is a single bond; a substituted or unsubstituted C1 to C30 alkylenegroup; a substituted or unsubstituted C2 to C30 alkenylene group; or asubstituted or unsubstituted C1 to C30 alkylene group or a substitutedor unsubstituted C2 to C30 alkenylene group wherein a methylene (—CH₂—)is replaced by a sulfonyl (—S(═O)₂—) moiety, a carbonyl (—C(═O)—)moiety, an ether (—O—) moiety, a sulfide (—S—) moiety, a sulfoxide(—S(═O)—) moiety, an ester (—C(═O)O—) moiety, an amide (—C(═O)NR—)moiety (wherein R is hydrogen or a C1 to C10 linear or branched alkylgroup), an imine moiety (—NR—) (wherein R is hydrogen or a C1 to C10linear or branched alkyl group), or a combination thereof,

m is an integer of 1 or greater,

k1 is 0 or an integer of 1 or greater, k2 is an integer of 1 or greater,and

a sum of m and k2 is an integer of 3 or greater,

provided that m does not exceed the valence of Y₁ and a sum of k1 and k2does not exceed the valence of L₁.

In an embodiment, a quantum dot polymer composite includes a polymermatrix; and the aforementioned quantum dot in the polymer matrix.

The polymer matrix may include a crosslinked polymer, a binder polymerincluding a carboxylic acid group, or a combination thereof.

The polymer matrix may include a binder polymer, a polymerizationproduct of a photopolymerizable monomer including at least carbon-carbondouble bond, a polymerization product of the photopolymerizable monomerand a multi-thiol compound including thiol groups at its terminal end,i.e., at a terminal end of the multi-thiol compound, or a combinationthereof.

In an embodiment, a display device includes a light source and a lightemitting element, wherein the light emitting element includes theaforementioned quantum dot-polymer composite and the light source isconfigured to provide the light emitting element with incident light.

The incident light may have a luminescence peak wavelength of about 440nanometers to about 460 nanometers.

In an embodiment, the light emitting element may include a sheetincluding the quantum dot polymer composite.

In an embodiment, the light emitting element may include a stackedstructure including a substrate and a light emitting layer disposed onthe substrate, wherein the light emitting layer includes a pattern ofthe quantum dot polymer composite and the pattern includes a repeatingsection configured to emit light at a predetermined wavelength.

The pattern may include a first section configured to emit first lightand a second section configured to emit a second light having a centerwavelength that is different from a center wavelength of the firstlight.

An embodiment provides an electronic device including the quantum dot.

The electronic device may include a light emitting diode (LED), anorganic light emitting diode (OLED), a sensor, a solar cell, an imagingsensor, or a liquid crystal display (LCD), but is not limited thereto.

Quantum dots of an embodiment may exhibit improved luminous propertiestogether with enhanced stability. A composition including theaforementioned quantum dots may provide improved processability. Thequantum dots may find uses in various display devices and biologicallabelling (e.g., bio sensor, bio imaging, etc.), a photo detector, asolar cell, a hybrid composite, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1A is an exploded view of a display device according to anembodiment;

FIG. 1B is a cross-sectional view of a device according to anembodiment;

FIG. 2 shows a process of producing a quantum dot polymer compositepattern using a composition according to an embodiment.

FIG. 3A is a cross-sectional view of a device according to anembodiment;

FIG. 3B is a cross-sectional view of a device according to anembodiment;

FIG. 4 is a cross-sectional view of a device according to an embodiment;

FIG. 5 is a schematic cross-sectional view showing an electroluminescentdevice according to an embodiment.

FIG. 6 is a schematic cross-sectional view showing an electroluminescentdevice according to an embodiment.

FIG. 7 is a UV-Vis absorption spectrum showing intensity (arbitraryunits (a.u.)) versus wavelength (nanometers (nm)) of the quantum dotsprepared in Example 1 and Comparative Example 1.

DETAILED DESCRIPTION

Advantages and characteristics of this disclosure, and a method forachieving the same, will become evident referring to the followingexample embodiments together with the drawings attached hereto. However,the embodiments should not be construed as being limited to theembodiments set forth herein. If not defined otherwise, all terms(including technical and scientific terms) in the specification may bedefined as commonly understood by one skilled in the art. The termsdefined in a generally-used dictionary may not be interpreted ideally orexaggeratedly unless clearly defined. In addition, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.

Further, the singular includes the plural unless mentioned otherwise.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

“About” as used herein is inclusive of the stated value and means withinan acceptable range of deviation for the particular value as determinedby one of ordinary skill in the art, considering the measurement inquestion and the error associated with measurement of the particularquantity (i.e., the limitations of the measurement system). For example,“about” can mean within one or more standard deviations, or within ±10%or 5% of the stated value.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer, or section from another element, component, region, layer, orsection. Thus, “a first element,” “component,” “region,” “layer,” or“section” discussed below could be termed a second element, component,region, layer, or section without departing from the teachings herein.

Furthermore, relative terms, such as “lower” and “upper,” may be usedherein to describe one element's relationship to another element asillustrated in the Figures. It will be understood that relative termsare intended to encompass different orientations of the device inaddition to the orientation depicted in the Figures. For example, if thedevice in one of the figures is turned over, elements described as beingon the “lower” side of other elements would then be oriented on “upper”sides of the other elements. The exemplary term “lower,” can therefore,encompasses both an orientation of “lower” and “upper,” depending on theparticular orientation of the figure. Similarly, if the device in one ofthe figures is turned over, elements described as “below” other elementswould then be oriented “above” the other elements. The exemplary terms“below” can, therefore, encompass both an orientation of above andbelow.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, unless a definition is otherwise provided, the term“substituted” refers to a compound or a group or a moiety wherein atleast one hydrogen atom thereof is substituted with a substituent. Thesubstituent may include a C1 to C30 alkyl group, a C2 to C30 alkenylgroup, a C2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30 heteroalkylgroup, a C3 to C30 heteroalkylaryl group, a C3 to C30 cycloalkyl group,a C3 to C15 cycloalkenyl group, a C6 to C30 cycloalkynyl group, a C2 toC30 heterocycloalkyl group, a halogen (—F, —Cl, —Br, or —I), a hydroxygroup (—OH), a nitro group (—NO₂), a cyano group (—CN), an amino group(—NRR′, wherein R and R′ are the same or different, and areindependently hydrogen or a C1 to C6 alkyl group), an azido group (—N₃),an amidino group (—C(═NH)NH₂), a hydrazino group (—NHNH₂), a hydrazonogroup (═N(NH₂)), an aldehyde group (—C(═O)H), a carbamoyl group(—C(O)NH₂), a thiol group (—SH), an ester group (—C(═O)OR, wherein R isa 01 to C6 alkyl group or a C6 to C12 aryl group), a carboxylic acidgroup (—COOH) or a salt thereof (—C(═O)OM, wherein M is an organic orinorganic cation), a sulfonic acid group (—SO₃H) or a salt thereof(—SO₃M, wherein M is an organic or inorganic cation), a phosphoric acidgroup (—PO₃H₂) or a salt thereof (—PO₃MH or —PO₃M₂, wherein M is anorganic or inorganic cation), or a combination thereof.

As used herein, unless a definition is otherwise provided, the term“hetero” means that the compound or group includes at least one (e.g.,one to three) heteroatom(s), wherein the heteroatom(s) is eachindependently N, O, S, Si, P, or a combination thereof.

As used herein, unless a definition is otherwise provided, the term“alkylene group” refers to a straight or branched chain, saturatedaliphatic hydrocarbon group having a valence of at least two. Thealkylene group may be optionally substituted with one or moresubstituents.

As used herein, unless a definition is otherwise provided, the term“arylene group” refers to a functional group having a valence of atleast two and formed by the removal of at least two hydrogen atoms fromone or more rings of an aromatic hydrocarbon, wherein the hydrogen atomsmay be removed from the same or different rings (preferably differentrings), each of which rings may be aromatic or nonaromatic. The arylenegroup may be optionally substituted with one or more substituents.

As used herein, unless a definition is otherwise provided, the term“aliphatic hydrocarbon group” refers to a C1 to C30 linear or branchedalkyl group, a C2 to C30 linear or branched alkenyl group, or C2 to C30linear or branched alkynyl group, the term “aromatic hydrocarbon group”refers to a C6 to C30 aryl group or a C2 to C30 heteroaryl group, andthe term “alicyclic hydrocarbon group” refers to a C3 to C30 cycloalkylgroup, a C3 to C30 cycloalkenyl group, or a C3 to C30 cycloalkynylgroup.

As used herein, unless a definition is otherwise provided, the term“(meth)acrylate” refers to acrylate, and/or methacrylate, or acombination thereof. The (meth)acrylate may include a (C1 to C10alkyl)acrylate, a (C1 to C10 alkyl)methacrylate, or a combinationthereof.

As used herein, unless a definition is otherwise provided, “alkoxy”means an alkyl group that is linked via an oxygen (i.e., alkyl-O—), forexample methoxy, ethoxy, and sec-butyloxy groups.

As used herein, unless a definition is otherwise provided, “alkyl” meansa straight or branched chain, saturated, monovalent hydrocarbon group(e.g., methyl or hexyl).

As used herein, unless a definition is otherwise provided, “alkynyl”means a straight or branched chain, monovalent hydrocarbon group havingat least one carbon-carbon triple bond (e.g., ethynyl).

As used herein, unless a definition is otherwise provided, “amine group”has the general formula —NRR, wherein each R is independently hydrogen,a C1-C12 alkyl group, a C7-C20 alkylarylene group, a C7-C20 arylalkylenegroup, or a C6-C18 aryl group.

As used herein, unless a definition is otherwise provided, “arene” meansa hydrocarbon having an aromatic ring, and includes monocyclic andpolycyclic hydrocarbons wherein the additional ring(s) of the polycyclichydrocarbon may be aromatic or nonaromatic. Specific arenes includebenzene, naphthalene, toluene, and xylene.

As used herein, unless a definition is otherwise provided, “aromatic”means an organic compound or group comprising at least one unsaturatedcyclic group having delocalized pi electrons. The term encompasses bothhydrocarbon aromatic compounds and heteroaromatic compounds.

As used herein, unless a definition is otherwise provided, “aryl” meansa monovalent group formed by the removal of one hydrogen atom from oneor more rings of an arene (e.g., phenyl or naphthyl).

As used herein, unless a definition is otherwise provided, “arylalkyl”means a substituted or unsubstituted aryl group covalently linked to analkyl group that is linked to a compound (e.g., a benzyl is a C7arylalkyl group).

As used herein, unless a definition is otherwise provided,“cycloalkenyl” means a monovalent group having one or more rings and oneor more carbon-carbon double bond in the ring, wherein all ring membersare carbon (e.g., cyclopentyl and cyclohexyl).

As used herein, unless a definition is otherwise provided, “cycloalkyl”means a monovalent group having one or more saturated rings in which allring members are carbon (e.g., cyclopentyl and cyclohexyl).

As used herein, unless a definition is otherwise provided,“cycloalkynyl” means a stable aliphatic monocyclic or polycyclic grouphaving at least one carbon-carbon triple bond, wherein all ring membersare carbon (e.g., cyclohexynyl).

As used herein, unless a definition is otherwise provided, “ester”refers to a group of the formula —O(C═O)Rx or a group of the formula—(C═O)ORx wherein Rx is 01 to C28 aromatic organic group or aliphaticorganic group. An ester group includes a C2 to C30 ester group, andspecifically a C2 to C18 ester group.

As used herein, unless a definition is otherwise provided, “heteroalkyl”is an alkyl group that comprises at least one heteroatom covalentlybonded to one or more carbon atoms of the alkyl group. Each heteroatomis independently chosen from nitrogen (N), oxygen (O), sulfur (S), andor phosphorus (P).

As used herein, unless a definition is otherwise provided, “ketone”refers to a C2 to C30 ketone group, and specifically a C2 to C18 ketonegroup. Ketone groups have the indicated number of carbon atoms, with thecarbon of the keto group being included in the numbered carbon atoms.For example a C2 ketone group is an acetyl group having the formulaCH3(C═O)—.

In an embodiment, “hydrophobic moiety” may be a moiety that may cause acompound including the same to agglomerate in an aqueous (hydrophilic)solution and to have a tendency to repel water. For example, thehydrophobic moiety may include an aliphatic hydrocarbon group (e.g.,alkyl, alkenyl, alkynyl, etc.) having at least one (e.g., at least two,three, four, five, or six, or higher) carbon atoms, an aromatichydrocarbon group having at least six carbon atoms (e.g., phenyl,naphthyl, arylalkyl group, etc.), or an alicyclic hydrocarbon grouphaving at least five carbon atoms (e.g., cyclohexyl, norbornenyl, etc.).

As used herein, a conversion efficiency (CE) refers to a ratio ofemission light amount of a quantum dot polymer composite with respect toa light amount absorbed by the composite from incident light (e.g., bluelight). The total light amount (B) of excitation light may be obtainedby integration of a photoluminescence (PL) spectrum of the incidentlight, the PL spectrum of the quantum dot-polymer composite film ismeasured to obtain a dose (A) of light in a green or red wavelengthregion emitted from the quantum dot-polymer composite film and a dose(B′) of incident light passing through the quantum dot-polymer compositefilm, and a conversion efficiency is calculated by the followingequation:

A/(B−B′)×100%=photoconversion efficiency(%)

In an embodiment, the term “dispersion” may refer to a system in which adispersed phase is a solid and a continuous phase includes a liquid. Forexample, the term “dispersion” may refer to a colloidal dispersion,wherein the dispersed phase includes particles having a dimension of atleast about 1 nm (e.g., at least about 2 nm, at least about 3 nm, or atleast about 4 nm) and less than or equal to about several micrometers(μm) (e.g., 2 μm or less, or 1 μm or less or 500 nm or less).

In the specification, the term “Group” in the term Group III, Group II,or the like refers to a group of the Periodic Table of Elements.

As used herein, “Group I” refers to Group IA and Group IB, and mayinclude Li, Na, K, Rb, and Cs but are not limited thereto.

As used herein, “Group II” refers to Group IIA and a Group IIB, andexamples of the Group II metal may include Cd, Zn, Hg, and Mg, but arenot limited thereto.

As used herein, “Group III” refers to Group IIIA and Group IIIB, andexamples of the Group III metal may include Al, In, Ga, and TI, but arenot limited thereto.

As used herein, “Group IV” refers to Group IVA and Group IVB, andexamples of the Group IV metal may include Si, Ge, and Sn but are notlimited thereto. As used herein, the term “a metal” may include asemi-metal such as Si.

As used herein, “Group V” refers to Group VA and may include nitrogen,phosphorus, arsenic, antimony, and bismuth but is not limited thereto.

As used herein, “Group VI” refers to Group VIA and may include sulfur,selenium, and tellurium, but is not limited thereto.

A semiconductor nanocrystal particle (also referred to as a quantum dot)is a nano-sized crystalline material. The semiconductor nanocrystalparticle may have a large surface area per unit volume due to arelatively small size of the semiconductor nanocrystal particle and mayexhibit different characteristics from bulk materials having the samecomposition due to a quantum confinement effect. Quantum dots may absorblight from an excitation source to be excited, and may emit energycorresponding to an energy bandgap of the quantum dots.

The quantum dots have potential applicability in various devices (e.g.,an electronic device) due to unique photoluminescence characteristics ofthe quantum dots. Quantum dots having properties currently applicable toan electronic device are mostly cadmium-based. However, cadmium maycause a serious environment/health problem and thus is a restrictedelement. As a type of cadmium free quantum dot, a Group III-V-basednanocrystal has been extensively researched. However, cadmium freequantum dots have technological drawbacks in comparison with cadmiumbased quantum dots. When the cadmium free quantum dots undergo variousprocesses for being applied to an electronic device, the cadmium freequantum dots may exhibit sharply deteriorated luminous properties.

In an embodiment, a quantum dot includes a core including a quaternaryalloy semiconductor nanocrystal and the quantum dot does not includecadmium. In an embodiment, the quaternary alloy semiconductornanocrystal includes indium (In), phosphorous (P), zinc (Zn), andselenium (Se), and in the core, a ratio of the zinc with respect to theindium is less than or equal to about 0.5:1 and in the core, a ratio ofselenium with respect to zinc is less than or equal to about 0.6:1.

A UV-Vis absorption spectrum of the core may have a first absorptionpeak wavelength of less than or equal to about 460 nm. In thisspecification, the term “first absorption peak” refers to a mainexcitonic peak appearing first from the longest wavelength region of aUV-Vis absorption spectrum of a quantum dot (i.e., appearing in thelowest energy region in the UV-Vis absorption spectrum).

By having the aforementioned structure and composition, the quantum dotof an embodiment may have an improved shell coating, and thereby, asingle quantum dot may show improved stability (e.g., thermal stability)and enhanced optical properties. Introducing, e.g., including, arelatively thick inorganic shell may increase the optical properties andthe stability of the quantum dots. For example, when a relatively thickZnSeS shell is coated on an indium phosphide core, a quantum yield mayincrease. However, the formation of the thick shell may result in agreater degree of a red-shift of the luminescent wavelength, in order toobtain a quantum dot emitting a green light with improved quantum yield,a core emitting light of a shorter wavelength (e.g., having a smallsize) may be desired. However, the core having a smaller size may bevulnerable to oxidation and have poor stability. Accordingly, thequantum dot emitting green light may be technologically limited in termsof photoluminescent quantum yield and stability.

The quantum dot of an embodiment includes a quaternary alloy corecomprising InPZnSe, thereby having a first absorption peak at awavelength of less than or equal to about 460 nm even when the core hasa relatively increased size. Therefore, disposing a shell of a desiredthickness on the aforementioned core makes it possible to provide agreen light emitting quantum dot having enhanced luminous properties andstability at the same time.

Without wishing to be bound by any theory, it is believed that byadopting the aforementioned alloy core, the quantum dot of an embodimentmay have a desired band gap alignment between the core and the shell andat the same time the lattice mismatch at the interface between the coreand the shell may be relieved/reduced and the amount of the phosphorous(P)-dangling bond on a surface of the core may decrease, which can makesit possible to achieve a stable epitaxial growth of the shell coating.

In an embodiment, the quantum dot includes an InPZnSe alloy core. Thequaternary alloy core or the quaternary alloy semiconductor nanocrystalparticle may not include sulfur.

In the core, a mole ratio of the zinc with respect to the indium may beless than or equal to about 0.5:1, for example, less than or equal toabout 0.49:1, less than or equal to about 0.48:1, less than or equal toabout 0.47:1, less than or equal to about 0.46:1, or less than or equalto about 0.45:1. In the core, a mole ratio of the zinc with respect tothe indium may be greater than or equal to about 0.29:1, for example,greater than or equal to about 0.3:1, greater than or equal to about0.35:1, greater than or equal to about 0.4:1, greater than or equal toabout 0.41:1, or greater than or equal to about 0.42:1.

In the core, a mole ratio of the selenium with respect to the zinc maybe less than or equal to about 0.6:1, for example, less than or equal toabout 0.59:1, less than or equal to about 0.58:1, less than or equal toabout 0.57:1, less than or equal to about 0.56:1, less than or equal toabout 0.55:1, less than or equal to about 0.54:1, less than or equal toabout 0.53:1, less than or equal to about 0.52:1, less than or equal toabout 0.51:1, less than or equal to about 0.50:1, or less than or equalto about 0.49:1. In the core, a mole ratio of the selenium with respectto the zinc may be greater than or equal to about 0.1:1, for example,greater than or equal to about 0.15:1, greater than or equal to about0.2:1, greater than or equal to about 0.25:1, greater than or equal toabout 0.3:1, or greater than or equal to about 0.4:1.

In the core, a mole ratio of the selenium with respect to the indium maybe greater than or equal to about 0.1:1, for example, greater than orequal to about 0.15:1 and less than or equal to about 0.3:1, forexample, less than or equal to about 0.25:1, or less than or equal toabout 0.21:1.

In the core, a ratio of total moles of the zinc and the selenium withrespect to total moles of the indium and the phosphorous (Zn+Se):(In+P)may be greater than or equal to about 0.2:1, for example, greater thanor equal to about 0.25, greater than or equal to about 0.3:1, greaterthan or equal to about 0.31:1, greater than or equal to about 0.32:1,greater than or equal to about 0.33:1, greater than or equal to about0.34:1, greater than or equal to about 0.35:1, or greater than or equalto about 0.36:1. The ratio of total moles of the zinc and the seleniumwith respect to total moles of the indium and the phosphorous may beless than or equal to about 0.65:1, for example, less than or equal toabout 0.6:1, less than or equal to about 0.5:1, less than or equal toabout 0.45:1, or less than or equal to about 0.4:1.

The quaternary alloy semiconductor nanocrystal may be a homogeneousalloy.

A size of the core may be greater than or equal to about 2 nm, forexample, greater than or equal to about 2.1 nm, or greater than or equalto about 2.2 nm. In an embodiment, the size of the core may be less thanor equal to about 3 nm, for example, less than or equal to about 2.7 nm.

The quantum dot may have a semiconductor nanocrystal shell on (e.g.,directly on) the core. The semiconductor nanocrystal shell may includezinc, selenium, and sulfur.

The semiconductor nanocrystal shell may include a first layer disposeddirectly on the core and including a first semiconductor nanocrystal anda second layer disposed on the first layer and including a secondsemiconductor nanocrystal having a composition different from that ofthe first semiconductor nanocrystal. An energy bandgap of the secondsemiconductor nanocrystal may be greater than or equal to that of thefirst semiconductor nanocrystal.

The first semiconductor nanocrystal may include zinc, selenium, andoptionally sulfur. The first semiconductor nanocrystal may include ZnSeor ZnSeS. The first semiconductor nanocrystal may not include thesulfur. A thickness of the first layer may be greater than or equal toabout 3 monolayers (MLs), or greater than or equal to about 4 MLs. Athickness of the first layer may be less than or equal to about 10 MLs,less than or equal to about 9 MLs, less than or equal to about 8 MLs, orless than or equal to about 7 MLs.

The second semiconductor nanocrystal may include zinc and sulfur. Thesecond semiconductor nanocrystal may not include selenium. The secondsemiconductor nanocrystal may include ZnS. The second semiconductornanocrystal shell may be disposed directly on the first semiconductornanocrystal shell. A thickness of the second layer may be selectedappropriately. The second layer may be an outermost layer of the quantumdot. The quantum dot of an embodiment has a core-multishell structure. Athickness of the second layer may be greater than or equal to about 1monolayer, for example, greater than or equal to about 2 MLs, greaterthan or equal to about 3 MLs, or greater than or equal to about 4 MLsand less than or equal to about 10 MLs, for example, less than or equalto about 9 MLs, less than or equal to about 8 MLs, less than or equal toabout 7 MLs, less than or equal to about 6 MLs, or less than or equal toabout 5 MLs.

In the core-shell quantum dot of an embodiment, a mole ratio of the zincwith respect to the indium may be greater than or equal to about 25:1,for example, greater than or equal to about 26:1, greater than or equalto about 27:1, greater than or equal to about 28:1, greater than orequal to about 29:1, greater than or equal to about 30:1, or greaterthan or equal to about 31:1 and less than or equal to about 45:1, forexample, less than or equal to about 44:1, less than or equal to about43:1, less than or equal to about 42:1, less than or equal to about41:1, or less than or equal to about 40:1.

In the core-shell quantum dot of an embodiment, a mole ratio of theselenium with respect to the indium may be greater than or equal toabout 5:1, for example, greater than or equal to about 6:1, greater thanor equal to about 7:1, greater than or equal to about 8:1, greater thanor equal to about 9:1, greater than or equal to about 10:1, greater thanor equal to about 11:1, greater than or equal to about 12:1, greaterthan or equal to about 13:1, or greater than or equal to about 14:1 andless than or equal to about 20:1, for example, less than or equal toabout 19:1, less than or equal to about 18:1, less than or equal toabout 17:1, less than or equal to about 16:1, or less than or equal toabout 15:1.

In the core-shell quantum dot of an embodiment, a mole ratio of thesulfur with respect to the indium may be greater than or equal to about10:1, greater than or equal to about 11:1, greater than or equal toabout 12:1, greater than or equal to about 13:1, or greater than orequal to about 15:1 and less than or equal to about 25:1, for example,less than or equal to about 24:1, less than or equal to about 23:1, lessthan or equal to about 22:1, less than or equal to about 21:1, less thanor equal to about 20:1, less than or equal to about 19:1, less than orequal to about 18:1, or less than or equal to about 17:1.

In the core-shell quantum dot of an embodiment, a mole ratio of S withrespect to Se may be less than or equal to about 1.5:1, for example,less than or equal to about 1.4:1, less than or equal to about 1.3:1, orless than or equal to about 1.2:1. The mole ratio of S with respect toSe may be greater than or equal to about 0.8:1, for example, greaterthan or equal to about 0.9:1, or greater than or equal to about 1:1.

In an embodiment, the quantum dot having the semiconductor nanocrystalshell may show a 1^(st) absorption peak wavelength in a range of greaterthan about 450 nm and a photoluminescent peak thereof, in the UV-Visabsorption spectrum.

In an embodiment, in the case of a green light emitting quantum dot, thefirst UV absorption peak wavelength may be greater than or equal toabout 480 nm, greater than or equal to about 485 nm, greater than orequal to about 490 nm and less than or equal to about 520 nm, less thanor equal to about 515 nm, or less than or equal to about 510 nm. In thecase of a red light emitting quantum dot, the first UV absorption peakwavelength may be greater than or equal to about 580 nm, for example,greater than or equal to about 590 nm, and less than or equal to about620 nm, for example, less than or equal to about 610 nm.

In an embodiment, the quantum dot having the semiconductor nanocrystalshell may emit light of a visible light wavelength region. The quantumdot of an embodiment may emit green light having a photoluminescent peakwavelength in a region of greater than or equal to about 500 nm, forexample, greater than or equal to about 510 nm, or greater than or equalto about 520 nm and less than or equal to about 560 nm, for example,less than or equal to about 550 nm. The quantum dot of an embodiment mayemit red light having a photoluminescent peak wavelength in a region ofgreater than or equal to about 600 nm, for example, greater than orequal to about 610 nm and less than or equal to about 650 nm, forexample, less than or equal to about 640 nm, or less than or equal toabout 630 nm.

The quantum dot may exhibit an improved level of a light emittingproperty. In an embodiment, the quantum yield of the quantum dot may begreater than or equal to about 70%, greater than or equal to about 75%,greater than or equal to about 80%, or greater than or equal to about85%. In an embodiment, a full width at half maximum of a maximumluminescent peak of the quantum dot may be less than or equal to about45 nm, for example, less than or equal to about 44 nm, less than orequal to about 43 nm, less than or equal to about 42 nm, or less than orequal to about 41 nm. In an embodiment, the quantum dot having thesemiconductor nanocrystal shell may have a size of greater than or equalto about 2 nm, greater than or equal to about 3 nm, greater than orequal to about 4 nm, or greater than or equal to about 5 nm. In anembodiment, the quantum dot may have a size of less than or equal toabout 30 nm, for example, less than or equal to about 25 nm, less thanor equal to about 24 nm, less than or equal to about 23 nm, less than orequal to about 22 nm, less than or equal to about 21 nm, less than orequal to about 20 nm, less than or equal to about 19 nm, less than orequal to about 18 nm, less than or equal to about 17 nm, less than orequal to about 15 nm, less than or equal to about 14 nm, less than orequal to about 13 nm, less than or equal to about 12 nm, less than orequal to about 11 nm, less than or equal to about 10 nm, less than orequal to about 9 nm, less than or equal to about 8 nm, or less than orequal to about 7 nm. The size of the quantum dot may be a diameter. Whenthe quantum dot is a non-spherically shaped particle, the size may be adiameter of a circle of equivalent area calculated from a twodimensional area of an electron microscopic image of the particle. Thesize of the quantum dot may be determined by for example, a TransmissionElectron Microscopic analysis, but it is not limited thereto.

A shape of the quantum dot is not particularly limited, may for examplebe a spherical, polyhedron, pyramid, multipod, or cube shape, nanotube,nanowire, nanofiber, nanosheet, or a combination thereof, but is notlimited thereto.

The quantum dot may include the organic ligand, the organic solvent, ora combination thereof, which will be described below, on a surface ofthe quantum dot. The organic ligand, the organic solvent, or acombination thereof may be bound to the surface of the quantum dot.

In an embodiment, a method of producing the aforementioned quantum dotincludes:

preparing a reaction liquid including an organic ligand, an indiumprecursor, a zinc precursor, a selenium precursor, and a phosphorousprecursor in an organic solvent; and

conducting a reaction in the reaction liquid at a temperature of aboutgreater than or equal to about 290° C. for a time period of less than orequal to about 1 hour to obtain a core including a quaternary alloysemiconductor nanocrystal (hereinafter, also referred to as an alloycore).

The preparation of the reaction liquid may include mixing the indiumprecursor and the zinc precursor in the organic solvent in the presenceof the organic ligand to obtain a mixture; and heating the mixture at atemperature of greater than or equal to about 150° C. (for example,greater than or equal to about 170° C., greater than or equal to about180° C., or greater than or equal to about 190° C.) and less than orequal to about 220° C. (for example, less than or equal to about 210°C.) and adding the selenium precursor and the phosphorous precursorthereto.

Details of the core including the quaternary alloy semiconductornanocrystal are the same as set forth above. The reaction liquid may notinclude an alkyl thiol. In an embodiment, the alloy core may be formedby a hot injection method wherein a phosphorous precursor and a seleniumprecursor are injected after the mixture is heated at a high temperature(at a temperature of greater than or equal to about 150° C.).

The indium precursor is not particularly limited and may be selectedappropriately. In an embodiment, the indium precursor may include anindium metal powder, an alkylated indium (e.g., dimethyl indium, diethylindium), an indium alkoxide, an indium carboxylate (e.g., indiumacetate), an indium carbonate, an indium nitrate, an indium perchlorate,an indium sulfate, an indium acetylacetonate, an indium halide (e.g.,indium chloride, indium bromide, indium iodide, indium fluoride), anindium cyanide, an indium hydroxide, an indium oxide, an indiumperoxide, or a combination thereof.

The zinc precursor is not particularly limited and may be selectedappropriately. In an embodiment, the zinc precursor may include a Znmetal powder, an alkylated Zn compound (e.g., dimethyl zinc, diethylzinc, or a combination thereof), a Zn alkoxide, a Zn carboxylate (e.g.,zinc acetate), a zinc carbonate, a Zn nitrate, a Zn perchlorate, a Znsulfate, a Zn acetylacetonate, a Zn halide (e.g., zinc chloride, zincbromide, zinc iodide, zinc fluoride, or a combination thereof), a Zncarbonate, a Zn cyanide, a Zn hydroxide, a Zn oxide, a Zn peroxide, or acombination thereof.

The selenium precursor is not particularly limited and may be desirablyselected. In an embodiment, the selenium precursor includesselenium-trioctyl phosphine (Se-TOP), selenium-tributyl phosphine(Se-TBP), selenium-triphenyl phosphine (Se-TPP),tellurium-tributylphosphine (Te-TBP), or a combination thereof but isnot limited thereto.

The phosphorous precursor is not particularly limited and may bedesirably selected. In an embodiment, the phosphorous precursor mayinclude tris(trimethylsilyl) phosphine, tris(dimethylamino) phosphine,triethylphosphine, tributylphosphine, trioctylphosphine,triphenylphosphine, tricyclohexylphosphine, or a combination thereof,but is not limited thereto.

The organic ligand may include RCOOH, RNH₂, R₂NH, R₃N, RSH, RH₂PO,R₂HPO, R₃PO, RH₂P, R₂HP, R₃P, ROH, RCOOR′, RPO(OH)₂, RHPOOH, RHPOOH(wherein R and R′ are the same or different, and are independently ahydrogen, a C1 to C40 (or C3 to C24) aliphatic hydrocarbon group (e.g.,a alkyl group, a alkenyl group, or a alkynyl group), a C6 to C40aromatic hydrocarbon group (such as a C6 to C20 aryl group), a polymericorganic ligand, or a combination thereof.

The organic ligand may coordinate to, e.g., be bound to, the surface ofthe obtained nanocrystal and help the nanocrystal to be well dispersedin the solution, and/or may affect light emitting and electricalcharacteristics of quantum dots, or a combination thereof.

Examples of the organic ligand may include methane thiol, ethane thiol,propane thiol, butane thiol, pentane thiol, hexane thiol, octane thiol,dodecane thiol, hexadecane thiol, octadecane thiol, or benzyl thiol;methane amine, ethane amine, propane amine, butyl amine, pentyl amine,hexyl amine, octyl amine, dodecyl amine, hexadecyl amine, octadecylamine, dimethyl amine, diethyl amine, dipropyl amine; methanoic acid,ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoicacid, heptanoic acid, octanoic acid, dodecanoic acid, hexadecanoic acid,octadecanoic acid, oleic acid, or benzoic acid; phosphine such assubstituted or unsubstituted methyl phosphine (e.g., trimethylphosphine, methyldiphenyl phosphine, etc.), substituted or unsubstitutedethyl phosphine (e.g., triethyl phosphine, ethyldiphenyl phosphine,etc.), substituted or unsubstituted propyl phosphine, substituted orunsubstituted butyl phosphine, substituted or unsubstituted pentylphosphine, or substituted or unsubstituted octylphosphine (e.g.,trioctylphosphine (TOP)); phosphine oxide such as substituted orunsubstituted methyl phosphine oxide (e.g., trimethyl phosphine oxide,methyldiphenyl phosphine oxide, etc.), substituted or unsubstitutedethyl phosphine oxide (e.g., triethyl phosphine oxide, ethyldiphenylphosphine oxide, etc.), substituted or unsubstituted propyl phosphineoxide, substituted or unsubstituted butyl phosphine oxide, orsubstituted or unsubstituted octyl phosphine oxide (e.g.,trioctylphosphine oxide (TOPO); diphenyl phosphine, triphenyl phosphinecompound, or an oxide compound thereof; an alkylphosphinic acid, analkylphosphonic acid; or the like, but are not limited thereto. Theorganic ligand may be used alone or as a mixture of at least two ligandcompounds.

The solvent may a C6 to C22 primary amine such as hexadecylamine; a C6to C22 secondary amine such as dioctylamine; a C6 to C40 tertiary aminesuch as trioctylamine; a nitrogen-containing heterocyclic compound suchas pyridine; a C6 to C40 aliphatic hydrocarbon (e.g., alkane, alkene,alkyne, etc.) such as hexadecane, octadecane, octadecene, or squalane; aC6 to C30 aromatic hydrocarbon such as phenyldodecane,phenyltetradecane, or phenyl hexadecane; a phosphine substituted with aC6 to C22 alkyl group such as trioctylphosphine, a phosphine oxidesubstituted with a C6 to C22 alkyl group such as trioctylphosphineoxide; a C12 to C22 aromatic ether such as phenyl ether, or benzylether, or a combination thereof. Types and amounts of the solvent may beappropriately selected considering precursors and organic ligands.

In the reaction system, an amount of each of the precursors, a reactiontemperature, and a reaction time are controlled such that the core hasthe aforementioned composition and the aforementioned size.

The method may further include forming a semiconductor nanocrystal shellon the alloy core. Details of the semiconductor nanocrystal shell arethe same as set forth above.

The forming of the semiconductor nanocrystal shell may include:

obtaining a mixture including a first shell precursor containing a metal(e.g., zinc), an organic ligand, and an organic solvent;

optionally heating the mixture; and

injecting the core and a second precursor containing a chalcogen (e.g.,selenium, sulfur, or a combination thereof) to the (optionally heated)mixture and keeping the mixture at a reaction temperature for apredetermined time (e.g., for about 40 minutes or longer) to form asemiconductor nanocrystal shell on the core.

The first shell precursor may include a zinc precursor. The second shellprecursor may include a selenium precursor, a sulfur precursor, or acombination thereof. Details of the organic ligand, the organic solvent,the zinc precursor, and the selenium precursor are the same as set forthabove.

The sulfur precursor is not particularly limited and may be selectedappropriately. The sulfur precursor may include hexane thiol, octanethiol, decane thiol, dodecane thiol, hexadecane thiol, mercapto propylsilane, sulfur-trioctylphosphine (S-TOP), sulfur-tributylphosphine(S-TBP), sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine(S-TOA), trimethylsilyl sulfide, sulfide ammonium, sodium sulfide, or acombination thereof.

The forming of the semiconductor nanocrystal shell may include:

Injecting the second shell precursor and optionally the first shellprecursor at least two times into a reaction system and keeping atemperature thereof at the reaction temperature for a predeterminedperiod of time to form a first layer disposed (directly) on the alloycore and including a first semiconductor nanocrystal (e.g., ZnSe), andthen forming a second layer including a second semiconductor nanocrystal(e.g., ZnS, ZnSeS, or a combination thereof) on the first layer.

The time period for the formation of the semiconductor nanocrystal shell(or each layer thereof) may be selected appropriately in light of adesired composition. In an embodiment, each of the time periods forforming the semiconductor nanocrystal shell (or the first layer thereof,the second layer thereof, or a combination thereof) may be greater thanor equal to about 40 minutes, for example, greater than or equal toabout 50 minutes, greater than or equal to about 60 minutes, greaterthan or equal to about 70 minutes, greater than or equal to about 80minutes, or greater than or equal to about 90 minutes and less than orequal to about 4 hours, for example, less than or equal to about 3hours, or less than or equal to about 2 hours. The reaction temperaturefor forming the shell may be selected appropriately. In an embodiment,the reaction temperature may be greater than or equal to about 280° C.,greater than or equal to about 290° C., greater than or equal to about300° C., greater than or equal to about 310° C., or greater than orequal to about 315° C. and less than or equal to about 350° C., lessthan or equal to about 340° C., or less than or equal to about 335° C.

In an embodiment wherein the quantum dot includes a first layerincluding ZnSe or ZnSeS on the aforementioned alloy core, and a secondlayer including ZnS, the semiconductor nanocrystal shell may be formedby obtaining a mixture including a zinc precursor, an organic ligand,and an organic solvent, optionally heating the mixture, and injectinginto the optionally heated mixture the alloy core, a predeterminedamount of a selenium precursor, (and optionally a predetermined amountof a sulfur precursor) and keeping a resulting mixture at a reactiontemperature for a predetermined time (e.g., of at least 40 minutes) toform the first layer on the alloy core, then injecting a zinc precursorand a sulfur precursor (and optionally a selenium precursor) thereto andkeep the same at a reaction temperature for another predetermined time(e.g., at least 40 minutes) to form a second layer on the first layer.In an embodiment, a reaction system for the formation of the secondlayer may not include a selenium precursor.

In an embodiment, in a reaction system for forming the first layer orthe second layer, a concentration of the sulfur precursor or theselenium precursor may be changed (decreased) during the reaction timeso that in the first layer or the second layer, a concentration of thesulfur or the selenium may change in a radial direction of the quantumdot.

The method may not include cooling the reaction solution including aparticle having the first semiconductor nanocrystal shell down to atemperature below 100° C. (for example, of less than or equal to about50° C., of less than or equal to about 30° C. or down to roomtemperature).

When the non-solvent is added into the obtained final reaction solution,the organic ligand-coordinated nanocrystal may be separated (e.g.,precipitated). The non-solvent may be a polar solvent that is misciblewith the solvent used in the reaction and nanocrystals are notdispersible therein. The non-solvent may be selected depending on thesolvent used in the reaction and may be for example, acetone, ethanol,butanol, isopropanol, ethanediol, water, tetrahydrofuran (THF), dimethylsulfoxide (DMSO), diethyl ether, formaldehyde, acetaldehyde, a solventhaving a similar solubility parameter to the foregoing solvents, or acombination thereof. The separation may be performed through acentrifugation, precipitation, chromatography, or distillation. Theseparated nanocrystal may be added to a washing solvent and washed, ifdesired. The washing solvent is not particularly limited and may includea solvent having a similar solubility parameter to that of the ligandand may, for example, include hexane, heptane, octane, chloroform,toluene, benzene, or the like.

The quantum dots may be dispersed in a dispersing solvent. The quantumdots may form an organic solvent dispersion. The organic solventdispersion may be free of water, may be free of a water miscible organicsolvent, or a combination thereof. The dispersing solvent may beselected appropriately. The dispersing solvent may include (or consistsof) the aforementioned organic solvent. The dispersing solvent mayinclude (or consists of) a substituted or unsubstituted C1 to C40aliphatic hydrocarbon, a substituted or unsubstituted C6 to C40 aromatichydrocarbon, or a combination thereof.

In an embodiment, a quantum dot composition includes: the aforementioned(cadmium free) quantum dots; a dispersing agent for dispersing thequantum dot (e.g., a binder polymer including a carboxylic acid group);a polymerizable (e.g., photopolymerizable) monomer including acarbon-carbon double bond; and optionally an initiator (e.g., aphotoinitiator or a thermal initiator). The composition may furtherinclude an organic solvent, and/or a liquid vehicle, or a combinationthereof. The composition may be photosensitive.

The composition of an embodiment may be used for a pattern of a quantumdot polymer composite. In an embodiment, the composition may be aphotoresist composition that may be applicable to a photolithographyprocess. In other embodiments, the composition may be an ink compositionthat may be applicable to an ink jet process (e.g., a liquid dropdischarging method such as an ink jet printing). In an embodiment, thecomposition may not include a conjugated polymer (except for a cardobinder that will be described below). In an embodiment, the compositionmay include a conjugated polymer. As used herein, the conjugated polymermay be a polymer having a conjugated double bond such as a polyphenylenevinylene.

In the composition, details for the (cadmium free) quantum dots are thesame as set forth above. In the composition, the amount of the quantumdot may be selected appropriately in light of the types and amounts ofother components in the composition and a final use thereof. In anembodiment, the amount of the quantum dot may be greater than or equalto about 1 weight percent (wt %), for example, greater than or equal toabout 2 wt %, greater than or equal to about 3 wt %, greater than orequal to about 4 wt %, greater than or equal to about 5 wt %, greaterthan or equal to about 6 wt %, greater than or equal to about 7 wt %,greater than or equal to about 8 wt %, greater than or equal to about 9wt %, greater than or equal to about 10 wt %, greater than or equal toabout 15 wt %, greater than or equal to about 20 wt %, greater than orequal to about 25 wt %, greater than or equal to about 30 wt %, greaterthan or equal to about 35 wt %, or greater than or equal to about 40 wt%, based on a total solid content of the composition. The amount of thequantum dot may be less than or equal to about 70 wt %, for example,less than or equal to about 65 wt %, less than or equal to about 60 wt%, less than or equal to about 55 wt %, or less than or equal to about50 wt %, based on a total solid content of the composition. A weightpercent of a component based on a total solid content of the compositionmay represent the amount of the component in the composite, which willbe described below.

In the composition of an embodiment, a dispersing agent is a compoundcapable of dispersing the quantum dots. The dispersing agent may be abinder polymer including a carboxylic acid group (for example, inrepeating units of the binder polymer). The binder polymer may be an(electrically) insulative polymer.

In an embodiment, the binder polymer may include:

a copolymer of a monomer combination including a first monomer, a secondmonomer, and optionally a third monomer, the first monomer including acarboxylic acid group and a carbon-carbon double bond, the secondmonomer including a carbon-carbon double bond and a hydrophobic moietyand not including a carboxylic acid group, and the third monomerincluding a carbon-carbon double bond and a hydrophilic moiety and notincluding a carboxylic acid group;

a multi-aromatic ring-containing polymer including a carboxylic acidgroup (—COOH) and having a backbone structure in a main chain (e.g., abackbone structure incorporated in the main chain), wherein the backbonestructure includes a cyclic group including a quaternary carbon atom andtwo aromatic rings bound to the quaternary carbon atom (e.g., also knownas a cardo binder);

or a combination thereof.

Examples of the first monomer may include, but are not limited to,acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaricacid, 3-butenoic acid, and other carboxylic acid vinyl ester compounds.The first monomer may include one or more compounds.

Examples of the second monomer may include, but are not limited to:

alkenyl aromatic compounds such as styrene, α-methyl styrene, vinyltoluene, or vinyl benzyl methyl ether;

unsaturated carboxylic acid ester compounds such as methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate,butyl methacrylate, benzyl acrylate, benzyl methacrylate, cyclohexylacrylate, cyclohexyl methacrylate, phenyl acrylate, or phenylmethacrylate;

unsaturated carboxylic acid amino alkyl ester compounds such as 2-aminoethyl acrylate, 2-amino ethyl methacrylate, 2-dimethyl amino ethylacrylate, or 2-dimethyl amino ethyl methacrylate;

maleimides such as N-phenylmaleimide, N-benzylmaleimide, orN-alkylmaleimide,

unsaturated carboxylic acid glycidyl ester compounds such as glycidylacrylate or glycidyl methacrylate;

vinyl cyanide compounds such as acrylonitrile or methacrylonitrile; and

unsaturated amide compounds such as acrylamide or methacrylamide,

but are not limited thereto.

As the second monomer, one or more compounds may be used.

If present, examples of the third monomer may include 2-hydroxy ethylacrylate, 2-hydroxy ethyl methacrylate, hydroxy propyl acrylate, hydroxypropyl methacrylate, 2-hydroxy butyl acrylate, and 2-hydroxy butylmethacrylate, but are not limited thereto. The third monomer may includeone or more compounds.

In an embodiment, in the binder polymer, an amount of a first repeatingunit derived from the first monomer may be greater than or equal toabout 5 mole percent (mol %), for example, greater than or equal toabout 10 mol %, greater than or equal to about 15 mol %, greater than orequal to about 25 mol %, or greater than or equal to about 35 mol %. Inthe binder polymer, an amount of the first repeating unit may be lessthan or equal to about 95 mol %, for example, less than or equal toabout 90 mol %, less than or equal to about 89 mol %, less than or equalto about 88 mol %, less than or equal to about 87 mol %, less than orequal to about 86 mol %, less than or equal to about 85 mol %, less thanor equal to about 80 mol %, less than or equal to about 70 mol %, lessthan or equal to about 60 mol %, less than or equal to about 50 mol %,less than or equal to about 40 mol %, less than or equal to about 35 mol%, or less than or equal to about 25 mol %.

In the binder polymer, an amount of a second repeating unit derived fromthe second monomer may be greater than or equal to about 5 mol %, forexample, greater than or equal to about 10 mol %, greater than or equalto about 15 mol %, greater than or equal to about 25 mol %, or greaterthan or equal to about 35 mol %. In the binder polymer, an amount of thesecond repeating unit may be less than or equal to about 95 mol %, forexample, less than or equal to about 90 mol %, less than or equal toabout 89 mol %, less than or equal to about 88 mol %, less than or equalto about 87 mol %, less than or equal to about 86 mol %, less than orequal to about 85 mol %, less than or equal to about 80 mol %, less thanor equal to about 70 mol %, less than or equal to about 60 mol %, lessthan or equal to about 50 mol %, less than or equal to about 40 mol %,less than or equal to about 35 mol %, or less than or equal to about 25mol %.

If present, in the binder polymer, an amount of a third repeating unitderived from the third monomer, when present, may be greater than orequal to about 1 mol %, for example, greater than or equal to about 5mol %, greater than or equal to about 10 mol %, or greater than or equalto about 15 mol %. In the binder polymer, an amount of the thirdrepeating unit, when present, may be less than or equal to about 30 mol%, for example, less than or equal to about 25 mol %, less than or equalto about 20 mol %, less than or equal to about 18 mol %, less than orequal to about 15 mol %, or less than or equal to about 10 mol %.

In an embodiment, the binder polymer may include a copolymer of(meth)acrylic acid and at least one second or third monomer including a(C6-C9 aryl) or (C1-C10 alkyl)(meth)acrylate, hydroxyl(C1-C10 alkyl)(meth)acrylate, or styrene. For example, the binder polymer may includea (meth)acrylic acid/methyl (meth)acrylate copolymer, a (meth)acrylicacid/benzyl (meth)acrylate copolymer, a (meth)acrylic acid/benzyl(meth)acrylate/styrene copolymer, a (meth)acrylic acid/benzyl(meth)acrylate/2-hydroxy ethyl (meth)acrylate copolymer, a (meth)acrylicacid/benzyl (meth)acrylate/styrene/2-hydroxy ethyl (meth)acrylatecopolymer, or a combination thereof.

In an embodiment, the binder polymer may include a multi-aromaticring-containing polymer. The multi-aromatic ring-containing polymer isalso known as a cardo binder, which may be commercially available.

The carboxylic acid group-containing binder may have an acid value ofgreater than or equal to about 50 mg KOH/g. For example, the carboxylicacid group-containing binder may have an acid value of greater than orequal to about 60 mg KOH/g, greater than or equal to about 70 mg KOH/g,greater than or equal to about 80 mg KOH/g, greater than or equal toabout 90 mg KOH/g, greater than or equal to about 100 mg KOH/g, greaterthan or equal to about 110 mg KOH/g, greater than or equal to about 120mg KOH/g, greater than or equal to about 125 mg KOH/g, or greater thanor equal to about 130 mg KOH/g, but is not limited thereto. Thecarboxylic acid group-containing binder may have an acid value of lessthan or equal to about 250 mg KOH/g, for example, less than or equal toabout 240 mg KOH/g, less than or equal to about 230 mg KOH/g, less thanor equal to about 220 mg KOH/g, less than or equal to about 210 mgKOH/g, less than or equal to about 200 mg KOH/g, less than or equal toabout 190 mg KOH/g, less than or equal to about 180 mg KOH/g, or lessthan or equal to about 160 mg KOH/g, but is not limited thereto.

The binder polymer (e.g., containing the carboxylic acid group, such asthe carboxylic acid group-containing binder) may have a molecular weightof greater than or equal to about 1,000 grams per mole (g/mol), forexample, greater than or equal to about 2,000 g/mol, greater than orequal to about 3,000 g/mol, or greater than or equal to about 5,000g/mol. The binder polymer may have a molecular weight of less than orequal to about 100,000 g/mol, for example, less than or equal to about50,000 g/mol or less than or equal to about 25,000 g/mol.

In the composition, an amount of the dispersing agent (e.g., the binderpolymer) may be greater than or equal to about 0.5 wt %, for example,greater than or equal to about 1 wt %, greater than or equal to about 5wt %, greater than or equal to about 10 wt %, greater than or equal toabout 15 wt %, or greater than or equal to about 20 wt %, based on atotal weight (or a total solid content) of the composition. In anembodiment, an amount of the carboxylic acid group-containing binder mayless than or equal to about 50 wt %, less than or equal to about 40 wt%, less than or equal to about 35 wt %, less than or equal to about 33wt %, or less than or equal to about 30 wt %, based on a total weight(or a total solid content) of the composition. The amount of the binderpolymer may be greater than or equal to about 0.5 wt % and less than orequal to about 55%.

In the composition according to an embodiment, the (photo)polymerizablemonomer including at least one (e.g., at least two, at least three, ormore) carbon-carbon double bond may include a (meth)acrylate monomer.Examples of the photopolymerizable monomer may include, but are notlimited to, a C1-C10-alkyl (meth)acrylate, ethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritoldi(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol di(meth)acrylate,dipentaerythritol tri(meth)acrylate, dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, bisphenol Aepoxy(meth)acrylate, bisphenol A di(meth)acrylate, trimethylolpropanetri(meth)acrylate, ethylene glycol monomethyl ether (meth)acrylate,novolac epoxy (meth)acrylate, propylene glycol di(meth)acrylate,tris(meth)acryloyloxyethyl phosphate, or a combination thereof.

The amount of the (photo)polymerizable monomer may be greater than orequal to about 0.5 wt %, for example, greater than or equal to about 1wt %, or greater than or equal to about 2 wt % with respect to a totalweight (or a total solid content) of the composition. The amount of thephotopolymerizable monomer may be less than or equal to about 50 wt %,for example, less than or equal to about 40 wt %, less than or equal toabout 30 wt %, less than or equal to about 28 wt %, less than or equalto about 25 wt %, less than or equal to about 23 wt %, less than orequal to about 20 wt %, less than or equal to about 18 wt %, less thanor equal to about 17 wt %, less than or equal to about 16 wt %, or lessthan or equal to about 15 wt % with respect to a total weight (or atotal solid content) of the composition.

The (photo) initiator included in the composition may be for thepolymerization of the (photo)polymerizable monomer. The initiator may bea compound that can generate a radical species under a mild condition(e.g., by light or heat) to promote the initiation of a radical reaction(e.g., a radical polymerization of a monomer). The initiator may be athermal initiator or a photoinitiator.

Examples of the thermal initiator may include azobisisobutyronitrile(AIBN), benzoyl peroxide (BPO) or the like but are not limited thereto.

The initiator is not particularly limited and may be selectedappropriately.

The photoinitiator may be a compound that can initiate a radicalpolymerization of the aforementioned photopolymerizable (e.g., acrylbased) monomer, a thiol compound that will be described below, or acombination thereof. The photoinitiator is not particularly limited. Thephotoinitiator may include a triazine compound, an acetophenonecompound, a benzophenone compound, a thioxanthone compound, a benzoincompound, an oxime compound, an aminoketone compound, a phosphine orphosphine oxide compound, a carbazole compound, a diketone compound, asulfonium borate compound, a diazo compound, a diimidazole compound, acarbazole compound, a diketone compound, a sulfonium borate compound, anazo compound (e.g., diazo compound), a biimidazole compound, or acombination thereof.

In the composition of an embodiment, an amount of the initiator may beadjusted in light of the types and the amount of the photopolymerizablemonomer as used. In an embodiment, the amount of the initiator may begreater than or equal to about 0.01 wt % or greater than or equal toabout 1 wt % and less than or equal to about 10 wt %, less than or equalto about 9 wt %, less than or equal to about 8 wt %, less than or equalto about 7 wt %, less than or equal to about 6 wt %, or less than orequal to about 5 wt % based on a total weight (or a total solid content)of the composition, but is not limited thereto.

The (photosensitive) composition may further include a thiol compound(e.g., a monothiol compound or a multi-thiol compound having two orgreater thiol groups), a metal oxide fine particle, or a combinationthereof.

When a plurality of metal oxide fine particles is present in the polymermatrix, the metal oxide fine particles may include TiO₂, SiO₂, BaTiO₃,Ba₂TiO₄, ZnO, or a combination thereof. An amount of the metal oxidefine particle may be less than or equal to about 50 wt %, less than orequal to about 40 wt %, less than or equal to about 30 wt %, less thanor equal to about 25 wt %, less than or equal to about 20 wt %, lessthan or equal to about 15 wt % and greater than or equal to about 1 wt%, or greater than or equal to about 5 wt % based on a total weight (ora total solid content) of the composition.

A particle size of the metal oxide fine particles is not particularlylimited and may be selected appropriately. The particle size of themetal oxide fine particles may be greater than or equal to about 100 nm,greater than or equal to about 150 nm, or greater than or equal to about200 nm and less than or equal to about 1,000 nm, less than or equal toabout 900 nm, or less than or equal to about 800 nm.

The multi-thiol compound may include a dithiol compound, a trithiolcompound, a tetrathiol compound, or a combination thereof. For example,the multi-thiol compound may include glycol di-3-mercaptopropionate(e.g., ethylene glycol di-3-mercaptopropionate), glycoldimercaptoacetate (e.g., ethylene glycol dimercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritoltetrakis(3-mercaptopropionate), pentaerythritoltetrakis(2-mercaptoacetate), 1,6-hexanedithiol, 1,3-propanedithiol,1,2-ethanedithiol, polyethylene glycol dithiol including 1 to 10ethylene glycol repeating units, or a combination thereof.

Based on a total weight (or a total solid content) of the composition,an amount of the thiol compound may be less than or equal to about 50 wt%, less than or equal to about 40 wt %, less than or equal to about 30wt %, less than or equal to about 20 wt %, less than or equal to about10 wt %, less than or equal to about 9 wt %, less than or equal to about8 wt %, less than or equal to about 7 wt %, less than or equal to about6 wt %, or less than or equal to about 5 wt %. The amount of the thiolcompound may be greater than or equal to about 0.1 wt %, for example,greater than or equal to about 0.5 wt %, greater than or equal to about1 wt %, greater than or equal to about 5 wt %, greater than or equal toabout 10 wt %, or greater than or equal to about 15 wt %, based on atotal weight (or a total solid content) of the composition.

The composition may further include an organic solvent, a liquidvehicle, or a combination thereof (hereinafter, simply referred to as“organic solvent”). The organic solvent, the liquid vehicle, or acombination thereof are not particularly limited. Types and amounts ofthe organic solvent may be appropriately selected by considering theaforementioned main components (i.e., the quantum dot, the COOHgroup-containing binder, the photopolymerizable monomer, thephotoinitiator, and if used, the thiol compound), and types and amountsof additives which will be described below. The composition may includea solvent in a residual amount except for a desired amount of the solidcontent (non-volatile components). The solvent may be appropriatelyselected by considering the other components (e.g., a binder, aphotopolymerizable monomer, a photoinitiator, and other additives) inthe composition, affinity for an alkali-developing solution, a boilingpoint, or the like. Non-limiting examples of the solvent and the liquidvehicle may include, but are not limited to: ethyl 3-ethoxy propionate;an ethylene glycol series such as ethylene glycol, diethylene glycol, orpolyethylene glycol; a glycol ether such as ethylene glycol monomethylether, ethylene glycol monoethyl ether, diethylene glycol monomethylether, ethylene glycol diethyl ether, or diethylene glycol dimethylether; glycol ether acetates such as ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycolmonoethyl ether acetate, or diethylene glycol monobutyl ether acetate; apropylene glycol series such as propylene glycol; a propylene glycolether such as propylene glycol monomethyl ether, propylene glycolmonoethyl ether, propylene glycol monopropyl ether, propylene glycolmonobutyl ether, propylene glycol dimethyl ether, dipropylene glycoldimethyl ether, propylene glycol diethyl ether, or dipropylene glycoldiethyl ether; a propylene glycol ether acetate such as propylene glycolmonomethyl ether acetate or dipropylene glycol monoethyl ether acetate;an amide such as N-methylpyrrolidone, dimethyl formamide, or dimethylacetamide; a ketone such as methyl ethyl ketone (MEK), methyl isobutylketone (MIBK), or cyclohexanone; a petroleum product such as toluene,xylene, or solvent naphtha; an ester such as ethyl acetate, propylacetate, butyl acetate, cyclohexyl acetate, or ethyl lactate; an ethersuch as diethyl ether, dipropyl ether, or dibutyl ether; chloroform, aC1 to C40 aliphatic hydrocarbon (e.g., alkane, alkene, or alkyne), ahalogen (e.g., chloro) substituted C1 to C40 aliphatic hydrocarbon(e.g., dichloroethane, trichloromethane, or the like), a C6 to C40aromatic hydrocarbon (e.g., toluene, xylene, or the like), a halogen(e.g., chloro) substituted C6 to C40 aromatic hydrocarbon, or acombination thereof.

The composition may further include various additives such as a lightdiffusing agent, a leveling agent, or a coupling agent, in addition tothe aforementioned components. The amount of the additive is notparticularly limited, and may be selected within an appropriate range,wherein the additive does not cause an adverse effect on the preparationof the composition, the preparation of the quantum dot polymercomposite, and optionally, the patterning of the composite. Types andexamples of the aforementioned additives may include any suitablecompound having a desired function and are not particularly limited.

If present, the amount of the additives may be, based on a total weightof the composition (or a solid content of the composition), greater thanor equal to about 0.1 wt %, for example, greater than or equal to about0.5 wt %, greater than or equal to about 1 wt %, greater than or equalto about 2 wt %, or greater than or equal to about 5 wt %, but it is notlimited thereto. If present, the amount of the additives may be lessthan or equal to about 20 wt %, for example, less than or equal to about19 wt %, less than or equal to about 18 wt %, less than or equal toabout 17 wt %, less than or equal to about 16 wt %, or less than orequal to about 15 wt %, but it is not limited thereto.

The composition may be prepared by mixing the aforementioned componentsappropriately. The composition may provide a quantum dot polymercomposite or a quantum dot pattern via polymerization (e.g.,photopolymerization).

In an embodiment, a quantum dot polymer composite may include a polymermatrix; and the aforementioned quantum dots dispersed in the polymermatrix.

The polymer matrix may include a thiolene resin, a linear or crosslinkedsubstituted or unsubstituted poly(meth)acrylate, a linear or crosslinkedsubstituted or unsubstituted polyurethane, a linear or crosslinkedsubstituted or unsubstituted epoxy resin, a linear or crosslinkedsubstituted or unsubstituted vinyl polymer, a linear or crosslinkedsubstituted or unsubstituted silicone resin, or a combination thereof.

In an embodiment, the polymer matrix may include a crosslinked polymer,a dispersing agent (for example, a binder polymer including a carboxylicacid group), or a combination thereof. The crosslinked polymer mayinclude a thiolene polymer, a crosslinked (meth)acrylate polymer, acrosslinked polyurethane, a crosslinked epoxy resin, a crosslinked vinylpolymer, a crosslinked silicone resin, or a combination thereof.

The polymer matrix may include a binder polymer; a polymerizationproduct of a photopolymerizable monomer including at least one (e.g., atleast two, three, four, or five or more) carbon-carbon double bond(s);optionally a polymerization product of the photopolymerizable monomerand a multi-thiol compound including at least two thiol groups at itsterminal ends; or a combination thereof. The polymer matrix may notinclude a conjugated polymer other than the cardo binder.

Details of the (cadmium free) quantum dot, the dispersing agent such asthe binder polymer, the photopolymerizable monomer, or the multi-thiolcompound are the same as set forth above.

The quantum dot polymer composite may be in a form of a film or a sheet.

The film of the quantum dot polymer composite or a pattern thereof mayhave, for example, a thickness of less than or equal to about 30 μm, forexample, less than or equal to about 10 μm, less than or equal to about8 μm, or less than or equal to about 7 μm and greater than about 2 μm,for example, greater than or equal to about 3 μm, greater than or equalto about 3.5 μm, or greater than or equal to about 4 μm.

The quantum dot polymer composite may exhibit improved thermalstability. Accordingly, the quantum dot polymer composite may exhibitphoto-conversion efficiency (PCE) of greater than or equal to about 20%when being heat-treated at about 180° C. for about 30 minutes under anitrogen atmosphere.

In an embodiment, a display device includes a light source and a lightemitting element (e.g., a photoluminescent element), and the lightemitting element includes the above quantum dot-polymer composite, andthe light source is configured to provide the light emitting elementwith incident light. The incident light may have a luminescence peakwavelength of greater than or equal to about 440 nm, for example,greater than or equal to about 450 nm and less than or equal to about460 nm.

In an embodiment, the light emitting element may include a sheet of thequantum dot polymer composite. The display device may further include aliquid crystal panel and the sheet of the quantum dot polymer compositemay be disposed between the light source and the liquid crystal panel.FIG. 1A shows an exploded view of a non-limiting display device.

Referring to FIG. 1A, the display device may have a structure wherein areflector, a light guide panel (LGP) and a blue LED light source(Blue-LED), the quantum dot-polymer composite sheet (QD sheet), forexample, various optical films such as a prism, double brightnessenhance film (DBEF), or the like are stacked and a liquid crystal (LC)panel is disposed thereon.

In an embodiment, the display device may not include a liquid crystallayer. The display device may include a blue organic light emittingdiode as a light source. Referring to FIG. 1B, the display deviceincludes a (blue) OLED as a light source, over which a quantum dotpolymer composite sheet including a mixture of red light emittingquantum dots (QDs) and green light emitting QDs. Over the quantum dotpolymer composite sheet, an absorption color filter layer havingred/green/blue sections and optionally a substrate may be disposed.

An organic light emitting diode may have at least two pixel electrodesformed on a substrate, a pixel define layer between adjacent pixelelectrodes, and an organic emission layer formed on each of the pixelelectrodes, a common electrode layer disposed over the organic emissionlayer.

The substrate may include an insulative material and may haveflexibility. Details of the substrate will be described below.

A line layer including a thin film transistor or the like is formed onthe substrate. The line layer may further include a gate line, a sustainvoltage line, a gate insulating layer, a data line, a source electrode,a drain electrode, a semiconductor, a protective layer, or the like. Thedetail structure of the line layer may be verified according to anembodiment. The gate line and the sustain voltage line are electricallyseparated from each other, and the data line is insulated and crossingthe gate line and the sustain voltage line. The gate electrode, thesource electrode, and the drain electrode form a control terminal, aninput terminal, and an output terminal of the thin film transistor,respectively. The drain electrode is electrically connected to the pixelelectrode.

The pixel electrode may function as an anode of the display device. Thepixel electrode may be formed of a transparent conductive material suchas indium tin oxide (ITO) or indium zinc oxide (IZO). The pixelelectrode 112 may be formed of a material having a light-blockingproperties such as gold (Au), platinum (Pt), nickel (Ni), tungsten (W),chromium (Cr), molybdenum (Mo), iron (Fe), cobalt Co), copper (Cu),palladium Pd), titanium (Ti), or the like. Alternatively, the pixelelectrode 112 may have a two-layered structure in which the transparentconductive material and the material having light-blocking propertiesare stacked sequentially.

Between two adjacent pixel electrodes, a pixel define layer (PDL)overlapped with a terminal end of the pixel electrode to divide thepixel electrode into a pixel unit. The pixel define layer is aninsulation layer which may electrically block the at least two pixelelectrodes.

The pixel define layer covers a portion of the upper surface of thepixel electrode, and the remaining region of the pixel electrode that isnot covered by the pixel define layer may provide an opening. An organicemission layer, which will be described below, may be formed on theregion defined by the opening.

The organic emission layer defines each pixel area by the pixelelectrode and the pixel define layer. In other words, one pixel area maybe defined as an area that is formed with one organic emission unitlayer which is contacted with one pixel electrode divided by the pixeldefine layer.

For example, in the display device according to an embodiment, theorganic emission layer may be defined as a first pixel area, a secondpixel area, and a third pixel area, and each pixel area is spaced apartfrom each other leaving a predetermined interval by the pixel definelayer.

In an embodiment, the organic emission layer may emit a third lightbelong to visible light region or belong to UV region. Each of the firstto the third pixel areas of the organic emission layer may emit thirdlight. In an embodiment, the third light may be a light having thehighest energy in the visible light region, for example, may be bluelight.

When all pixel areas of the organic emission layer are designed to emitthe same light, each pixel area of the organic emission layer may be allformed of the same or similar materials or may show the same or similarproperties. Thus it may significantly relieve a process difficulty offorming the organic emission layer, so the display device may be easilyapplied for the large scale/large area process. However, the organicemission layer according to an embodiment is not necessarily limitedthereto, but the organic emission layer may be designed to emit at leasttwo different lights.

The organic emission layer includes an organic emission unit layer ineach pixel area, and each organic emission unit layer may furtherinclude an auxiliary layer (e.g., hole injection layer (HIL), holetransport layer (HTL), electron transport layer (ETL), etc.) besides theemission layer.

The common electrode may function as a cathode of the display device 10.The common electrode 114 may be formed of a transparent conductivematerial such as indium tin oxide (ITO) or indium zinc oxide (IZO). Thecommon electrode may be formed on the organic emission layer and may beintegrated therewith.

A planarization layer or a passivation layer may be formed on the commonelectrode. The planarization layer may include an insulating materialfor providing electrical insulation with the common electrode.

An absorptive color filter layer may be formed corresponding to each ofthe pixel areas. The absorptive color filter layer may include a greensection that may selectively transmit green light with absorbing andblocking lights other than green light, a red section that mayselectively transmit red light with absorbing and blocking lights otherthan red light, and a blue section that may selectively transmit bluelight with absorbing and blocking green and red lights (e.g., lightshaving a wavelength of less than or equal to about 500 nm).

In other embodiments, the display device may include a stacked structureincluding a (e.g., transparent) substrate and a light emitting layer(e.g., a photoluminescent layer) disposed on the substrate as a lightemitting element.

In the stacked structure, the light emitting layer includes a pattern ofthe quantum dot polymer composite, and the pattern may include at leastone repeating section configured to emit light of a predeterminedwavelength.

The pattern of the quantum dot polymer composite may include a repeatingsection of a first section that may emit a first light, a second sectionthat may emit a second light, or a combination thereof.

The first light and the second light have a different maximumphotoluminescence peak wavelength in a photoluminescence spectrum. In anembodiment, the first light (R) may be red light present at a maximumphotoluminescence peak wavelength of about 600 nm to about 650 nm (e.g.,about 620 nm to about 650 nm), the second light (G) may be green lightpresent at a maximum photoluminescence peak wavelength of about 500 nmto about 550 nm (e.g., about 510 nm to about 550 nm), or vice versa(i.e., the first light may be a green light and the second light may bea red light).

A pattern of the quantum dot polymer composite may include a thirdsection that may emit or transmit a third light different from the firstand the second lights (e.g., blue light). The maximum peak wavelength ofthe third light may be greater than or equal to about 380 nm, greaterthan or equal to about 420 nm, greater than or equal to about 430 nm,greater than or equal to about 440 nm, or greater than or equal to about445 nm and less than or equal to about 480 nm, less than or equal toabout 470 nm, less than or equal to about 460 nm, or less than or equalto about 455 nm. The light source may emit the third light.

In a display device of an embodiment, a patterned film of the quantumdot polymer composite may include a first section emitting red light anda second section emitting green light, and the light source may emitblue light. On front surfaces (i.e., light extraction side) of the firstand the second sections, an optical element that may block (e.g.,reflect or absorb) blue light may be disposed.

The substrate may be a substrate including an insulation material. Thesubstrate may include a material such as glass; various polymers such asa polyester (e.g., poly(ethylene terephthalate) (PET), poly(ethylenenaphthalate) (PEN), or the like), a polycarbonate, a poly(C1 to C10alkyl (meth)acrylate), a polyimide, a polyamide, or a combinationthereof (e.g., a copolymer or a mixture thereof); a polysiloxane (e.g.,polydimethylsiloxane (PDMS)); an inorganic material such as Al₂O₃ orZnO; or a combination thereof, but is not limited thereto. A thicknessof the substrate may be desirably selected considering a substratematerial but is not particularly limited. The substrate may haveflexibility. The substrate may have a transmittance of greater than orequal to about 50%, greater than or equal to about 60%, greater than orequal to about 70%, greater than or equal to about 80%, or greater thanor equal to about 90% for light emitted from the quantum dot.

At least a portion of the substrate may have an additional element thatis configured to cut (absorb or reflect) blue light. A layer capable ofblocking (e.g., absorbing or reflecting) blue light, also referred toherein as a “blue cut layer” or “blue light absorption layer,” may bedisposed on at least one surface of the substrate. For example, a bluecut layer (blue light absorption layer) may include an organic materialand a predetermined dye, such as, for example, a yellow dye or a dyecapable of absorbing blue light and transmitting green and/or red light.

In an embodiment, a method of producing the stacked structure includes

forming a film of the above composition on a substrate;

exposing a selected region of the film to light (e.g., having awavelength of less than or equal to about 400 nm); and

developing the exposed film with an alkali developing solution to obtaina pattern of the quantum dot polymer composite.

Details of the substrate and the composition are the same as describedabove.

A non-limiting method of forming a pattern of the quantum dot polymercomposite is explained with reference to FIG. 2.

The composition is coated to have a predetermined thickness on asubstrate in an appropriate method of spin coating, slit coating, or thelike (S1). If desired, the formed film may be pre-baked (S2). Conditions(such as a temperature, duration, or an atmosphere) for the pre-bakingmay be selected appropriately.

The formed (and optionally, pre-baked) film is exposed to light of apredetermined wavelength (UV light) under a mask having a predeterminedpattern (S3). The wavelength and the intensity of light may be selecteddepending on the types and the amounts of the photoinitiator, the typesand the amounts of quantum dots, or the like.

The film having the exposed selected area is treated (e.g., sprayed orimmersed) with an alkali developing solution (S4), and thereby theunexposed region in the film is dissolved to provide a desired pattern.The obtained pattern may be post-baked (S5), if desired, to improvecrack resistance and solvent resistance of the pattern, for example, ata temperature of about 150° C. to about 230° C. for a predeterminedtime, for example, greater than or equal to about 10 min or greater thanor equal to about 20 min.

When the quantum dot-polymer composite pattern has a plurality ofrepeating sections, a quantum dot-polymer composite having a desiredpattern may be obtained by preparing a plurality of compositionsincluding a quantum dot (e.g., a red light emitting quantum dot, a greenquantum dot, or optionally, a blue quantum dot) having desiredphotoluminescence properties (a photoluminescence peak wavelength or thelike) to form each repeating section and repeating the pattern formationprocess for each of the composition as many times (e.g., two or moretimes or three or more times) as desired to form a desired pattern ofthe quantum dot polymer composite (S6).

For example, the quantum dot-polymer composite may be in the form of apattern of at least two different repeating color sections (e.g., RGBsections). Such a quantum dot-polymer composite pattern may be used as aphotoluminescence-type color filter in a display device.

In an embodiment, the aforementioned stacked structure may be formed byusing an ink composition that includes the quantum dots and the liquidvehicle. In such a method, a proper system (e.g., a liquid dischargedevice such as an ink jet or a nozzle printing device) is used todeposit the ink composition on a desired substrate or an organic lightemitting device (e.g., blue OLED) with a desired pattern, which is thenheated for the removal of the solvent and the polymerization. The inkjet process may provide a highly precise quantum dot polymer compositefilm or pattern within a short period of time in a simple manner In adisplay device that includes a light source and a light emitting elementincluding a stacked structure, the light source may be configured toprovide incident light to the light emitting element including thestacked structure. The incident light may have a wavelength of about 440nm to about 480 nm such as about 440 nm to about 470 nm. The incidentlight may be the third light.

For example, each light emitting unit of the light source may include anelectroluminescent device (e.g., an organic light emitting diode (OLED))configured to emit light of a predetermined wavelength (e.g., bluelight, green light, or a combination thereof). Structures and materialsof the electroluminescent device and the organic light emitting diode(OLED) are not particularly limited and may be selected appropriately.

FIG. 3A and FIG. 3B show a schematic cross-sectional view of a displayof an embodiment of a layered structure. Referring to FIG. 3A and FIG.3B, the light source may include an organic light emitting diode OLED.For example, the OLED may emit blue light or a light having a wavelengthin a region of about 500 nm or less.

Details of the organic light emitting diode OLED are the same as setforth above. The OLED may include (at least two) pixel electrodes 90 a,90 b, 90 c formed on a substrate 100, a pixel defining layer 150 a, 150b formed between the adjacent pixel electrodes 90 a, 90 b, 90 c, anorganic light emitting layer 140 a, 140 b, 140 c formed on the pixelelectrodes 90 a, 90 b, 90 c, and a common electrode layer 130 formed onthe organic light emitting layer 140 a, 140 b, 140 c.

The pixel areas of the OLED may be disposed corresponding to the first,second, and third sections that will be described in detail below,respectively.

The stacked structure that includes a quantum dot-polymer compositepattern 170 (e.g., including a first repeating section including greenlight emitting quantum dots, a second repeating section including redlight emitting quantum dots, or a combination thereof) and a substrate,or the quantum dot-polymer composite pattern 170, may be disposed on orover a light source, for example, directly on the light source.

The light (e.g., blue light) emitted from the light source may enter thesecond section 21 and the first section 11 of the pattern to emit (e.g.,converted) red light R and green light G, respectively. Blue light Bemitted from the light source passes through or transmits from the thirdsection 31. Over the second section 21 emitting red light, the firstsection 11 emitting green light, or a combination thereof, an opticalelement 160 may be disposed. The optical element may be a blue cut layerwhich cuts (e.g., reflects or absorbs) blue light and optionally greenlight, or a first optical filter. The blue cut layer 160 may be disposedon the upper substrate 240. The blue cut layer 160 may be disposedbetween the upper substrate 240 and the quantum dot-polymer compositepattern 170 and over the first section 11 and the second section 21.Details of the blue cut layer are the same as set forth for the firstoptical filter 310 below.

The aforementioned device may be fabricated by separately preparing thelayered structure and the OLED (for example, a blue OLED), respectively,and combining them. Alternatively, the device may be fabricated bydirectly forming the pattern of the quantum dot-polymer composite overthe OLED.

In an embodiment, the display device may further include a lowersubstrate 210, an optical element (e.g., polarizer) 300 disposed belowthe lower substrate 210, and a liquid crystal layer 220 interposedbetween the layered structure and the lower substrate 210. The layeredstructure may be disposed in such a manner that a light emitting layer(i.e., the quantum dot-polymer composite pattern 170) faces the liquidcrystal layer. The display device may further include an optical element(e.g., polarizer) 300 between the liquid crystal layer 220 and the lightemitting layer. The light source may further include an LED andoptionally a light guide panel.

FIG. 4 is a schematic view of a liquid crystal display device of anembodiment. Referring to FIG. 4, in an embodiment, the display deviceincludes a liquid crystal panel 200, an optical element 300 (e.g.,polarizer) disposed on the liquid crystal panel 200, under the liquidcrystal panel 200, or a combination thereof, and a backlight unitincluding a blue light emitting light source 110 under a lower opticalelement 300. The backlight unit may include a light source 110 and alight guide 120 (edge type). Alternatively, the backlight unit may be adirect light source without a light guide panel.

The liquid crystal panel 200 may include a lower substrate 210, a (e.g.,transparent and insulative) upper substrate 240, and a liquid crystallayer 220 between the upper and lower substrates, and a light emittinglayer (color filter layer) 230 disposed on or under the upper substrate240. The light emitting layer 230 may include the quantum dot-polymercomposite (or a pattern thereof).

The lower place 210 may be made of a transparent and insulativematerial. Details of the substrate are the same as set forth above. Awire plate 211 is provided on an internal surface, for example, on theupper surface of the lower substrate 210. The wire plate 211 may includea plurality of gate wires and data wires that define a pixel area, athin film transistor disposed adjacent to a crossing region of gatewires and data wires, and a pixel electrode for each pixel area, but isnot limited thereto. Details of the wire plate are not particularlylimited and may be selected appropriately.

The liquid crystal layer 220 may be disposed on the wire plate 211. Theliquid crystal layer 220 may include an alignment layer 221 on an uppersurface of the liquid crystal layer 220 and on a lower surface of theliquid crystal layer 220, to initially align the liquid crystal materialincluded therein. Details regarding a liquid crystal material, analignment layer material, a method of forming an alignment layer, amethod of forming a liquid crystal layer, a thickness of liquid crystallayer, or the like are not particularly limited and may be selectedappropriately.

In an embodiment, an upper optical element or an upper polarizer 300 maybe provided between the liquid crystal layer 220 and the upper substrate240, but it is not limited thereto. For example, the upper opticalelement or polarizer 300 may be disposed between the liquid crystallayer 220 (or a common electrode 231) and the light emitting layer (orthe quantum dot-polymer composite pattern). The upper polarizer may bedisposed on or over the transparent substrate 240. The polarizer may beany suitable polarizer that can be used in a liquid crystal displaydevice. The polarizer may be TAC (triacetyl cellulose) having athickness of less than or equal to about 200 μm, but is not limitedthereto. In an embodiment, the upper optical element may be a coatingthat controls a refractive index without a polarization function.

The backlight unit may include a light guide panel 120. In anembodiment, the backlight unit may be an edge-type lighting. Forexample, the backlight unit may include a reflector, a light guideprovided on the reflector and providing a planar light source with theliquid crystal panel 200, at least one optical sheet on the light guide,for example, a diffusion plate, a prism sheet, or the like, or acombination thereof, but is not limited thereto.

The backlight unit may not have a light guide panel. In an embodiment,the backlight unit may be a direct-type lighting. For example, thebacklight unit may have a reflector, and may have a plurality offluorescent lamps disposed on the upper side of the reflector at regularintervals, or may have an LED operating substrate on which a pluralityof light emitting diodes are disposed, and over them, a diffusion plateand optionally at least one optical sheet may be provided. Details(e.g., each components of light guide and various optical sheets, areflector, or the like) of such a backlight unit are known and are notparticularly limited.

A black matrix 241 may be provided under the upper substrate 240 (e.g.,on a lower surface thereof). Openings within the black matrix 241 arealigned with (or provided to hide) a gate line, a data line, and a thinfilm transistor of a wire plate 211 on the lower substrate 210. A secondsection (R) including a color filter emitting red light, a first section(G) including a color filter emitting green light, a third section (B)including a color filter for emitting or transmitting blue light, or acombination thereof may be disposed in the openings within the blackmatrix 241 (BM). For example, the black matrix 241 may have a latticeshape. If desired, the light emitting layer may further include at leastone fourth repeating section. The fourth section may be configured toemit light having a color (e.g., cyan, magenta, yellow, or the like)different from the colors of the light emitted from the first to thirdsections.

In the light emitting layer 230, the sections forming the pattern may berepeated corresponding to the pixel area formed on the lower substrate.The light emitting layer (color filter layer) 230 may be on atransparent common electrode 231.

The third section (B) configured to emit/transmit blue light may be atransparent color filter that does not change a light emitting spectrumof the light source. Blue light emitted from the backlight unit may passthe polarizer and the liquid crystal layer and then enter as a polarizedlight and go out as it is. If desired, the third section may includequantum dots emitting blue light.

If desired, the display device may further include a blue cut filter,hereinafter, also referred to as a first optical filter layer. The bluecut filter 310 may be disposed between upper surfaces of the secondsection (R) and the first section (G) and the lower surface of the uppersubstrate 240, or on an upper surface of the upper substrate (240). Theblue cut filter 310 may include a sheet having openings that correspondto the third section (B) (e.g., a pixel area showing, e.g., emitting, ablue color) and may be formed on portions corresponding to the first andsecond sections (G, R). The first optical filter layer 310 may be formedas a single body structure over the portions of the light emitting layer230 corresponding to the first and second sections (G, R), and which areother than the portions overlapping the third section, but is notlimited thereto. Alternatively, at least two first optical filter layersmay be spaced apart from each other and may be disposed over each of theportions overlapping the first and the second sections, respectively.

For example, the first optical filter layer may block light having apredetermined wavelength range in the visible light range and maytransmit light having another wavelength range. For example, the firstoptical filter layer may block blue light and transmit light other thanblue light. For example, the first optical filter layer may transmitgreen light, red light, or yellow light (e.g., the mixed light of thegreen light and the red light).

The first optical filter layer may include a polymer thin film includinga dye, a pigment, or a combination thereof that absorbs light having aspecific wavelength, i.e., the wavelength to be blocked. The firstoptical filter layer may block at least 80%, or at least 90%, even atleast 95% of blue light having a wavelength of less than or equal toabout 480 nm. With respect to the visible light having otherwavelengths, the first optical filter layer may have a lighttransmittance of greater than or equal to about 70%, for example,greater than or equal to about 80%, greater than or equal to about 90%,or even up to 100%.

The first optical filter layer may absorb and substantially block bluelight having a wavelength of less than or equal to about 500 nm, and forexample, may selectively transmit green light or red light. At least twofirst optical filter layers may be spaced apart and disposed on each ofthe portions overlapping the first and second sections, respectively.For example, the first optical filter layer selectively transmitting redlight may be disposed on the portion overlapping the section emittingred light and the first optical filter layer selectively transmittinggreen light may be disposed on the portion overlapping the sectionemitting green light.

In an embodiment, the first optical filter layer may include a firstregion, a second region, or a combination thereof. The first region ofthe first optical filter layer blocks (e.g., absorbs) blue light and redlight and transmits light having a wavelength of a predetermined range,e.g., a wavelength greater than or equal to about 500 nm, greater thanor equal to about 510 nm, or greater than or equal to about 515 nm, andless than or equal to about 550 nm, less than or equal to about 540 nm,less than or equal to about 535 nm, less than or equal to about 530 nm,less than or equal to about 525 nm, or less than or equal to about 520nm. The second region of the first optical filter layer blocks (e.g.,absorb) blue light and green light and transmits light having awavelength of a predetermined range, e.g., a wavelength of greater thanor equal to about 600 nm, greater than or equal to about 610 nm, orgreater than or equal to about 615 nm and less than or equal to about650 nm, less than or equal to about 640 nm, less than or equal to about635 nm, less than or equal to about 630 nm, less than or equal to about625 nm, or less than or equal to about 620 nm. The first region of thefirst optical filter layer may be disposed (directly) on or over alocation overlapping a green light emitting section and the secondregion of the first optical filter layer may be disposed (directly) onor over a location overlapping a red light emitting section. The firstregion and the second region may be optically isolated from one another,for example, by a black matrix. The first optical filter layer maycontribute to improving the color purity of a display device.

The first optical filter layer may be a reflection type filter includinga plurality of layers (e.g., inorganic material layers) each having adifferent refractive index. For example, in the first optical filterlayer, two layers having different refractive indices may be alternatelystacked on each other. For example, a layer having a high refractiveindex and a layer having a low refractive index may be alternatelylaminated with each other.

In the first optical filter layer, a thickness of the layer having ahigh refractive index and a thickness of the layer having a lowrefractive index and the stacked number thereof may be determineddepending upon a refractive index of each layer and the wavelength to bereflected. In an embodiment, for example, each layer having a highrefractive index in the first optical filter layer may have a thicknessin a range of about 3 nm to about 300 nm, and each layer having a lowrefractive index in the first optical filter layer may have a thicknessin a range of about 3 nm to about 300 nm.

A total thickness of the first optical filter layer may be in a rangeof, for example, about 3 nm to about 10,000 nm, about 300 nm to about10,000 nm, or about 1,000 nm to about 10,000 nm. Each of the layerhaving a high refractive index and the layer having a low refractiveindex in the first optical filter layer may have a same thickness andmaterial as each other or different thicknesses and materials from eachother.

The display device may further include a second optical filter layer 311(e.g., red/green light or yellow light recycling layer) that is disposedbetween the light emitting layer 230 and the liquid crystal layer 220,and between the light emitting layer 230 (e.g., the quantum dot polymercomposite layer) and the upper polarizer 300. The second optical filterlayer 311 may transmit at least a portion of a third light, and reflectat least a portion of a first light, a second light, or a combinationthereof. The second optical filter layer may reflect light having awavelength of greater than 500 nm. The first light may be green (or red)light, the second light may be red (or green) light, and the third lightmay be blue light.

In an embodiment the display device, the second optical filter layer maybe formed directly under the second planarization layer to provide arelatively planar surface.

In an embodiment, the second optical filter layer may include amonolayer having a low refractive index. In an embodiment, for example,the second optical filter layer may be a transparent thin film having arefractive index of less than or equal to about 1.4, less than or equalto about 1.3, or less than or equal to about 1.2.

The second optical filter layer having a low refractive index mayinclude, for example, a porous silicon oxide, a porous organic material,a porous organic/inorganic composite, or a combination thereof.

In an embodiment, the second optical filter layer may include aplurality of layers having different refractive indexes from each other.In an embodiment, for example, the second optical filter layer may beformed by alternatively stacking two layers having different refractiveindexes from each other, or may be formed by alternatively stacking amaterial having a high refractive index and a material having a lowrefractive index.

The layer having a high refractive index in the second optical filterlayer may include, for example, hafnium oxide, tantalum oxide, titaniumoxide, zirconium oxide, magnesium oxide, cesium oxide, lanthanum oxide,indium oxide, niobium oxide, aluminum oxide, silicon nitride, or acombination thereof, but not being limited thereto. In such anembodiment, the layer having a high refractive index in the secondoptical filter layer may include another material having a higherrefractive index than the layer having a low refractive index in thesecond optical filter layer.

The layer having a low refractive index in the second optical filterlayer may include, for example, a silicon oxide, but not being limitedthereto. In such an embodiment, the layer having a low refractive indexin the second optical filter layer may include another material having alower refractive index than the layer having a high refractive index inthe second optical filter layer.

As the refractive index difference between the layer having a highrefractive index and the layer having a low refractive index is thehigher, the second optical filter layer may have the higher selectivityto a wavelength.

In the second optical filter layer, each thickness of the layer having ahigh refractive index and the layer having a low refractive index andthe stacked number thereof may be determined depending upon a refractiveindex of each layer and the wavelength to be reflected.

In one embodiment, for example, each layer having a high refractiveindex in the second optical filter layer may have a thickness in a rangeof about 3 nm to about 300 nm, and each layer having a low refractiveindex in the second optical filter layer may have a thickness in a rangeof about 3 nm to about 300 nm. The total thickness of the second opticalfilter layer may be in a range of, for example, about 3 nm to about10,000 nm, about 300 nm to about 10,000 nm, or about 1,000 nm to about10,000 nm. Each of the layer having a high refractive index and thelayer having a low refractive index in the second optical filter layermay have a same thickness and material as each other or differentthicknesses and materials from each other.

In an embodiment, the second optical filter layer reflects at least aportion of the first light R and the second light G and transmits atleast a portion (e.g., entire) of the third light B. In an embodiment,the second optical filter layer may transmit only the third light B in ablue light wavelength region or a wavelength region of less than orequal to about 500 nm, and light in a wavelength region of greater thanabout 500 nm, which is a green light G, a yellow light, a red light R orthe like, may not be passed through the second optical filter layer butbe reflected. Thus, the reflected green and red lights may pass throughthe first and the second sections to be emitted to the outside of thedisplay device 10.

The second optical filter layer may reflect the light in a wavelengthregion of greater than about 500 nm with a reflectance of greater thanor equal to about 70%, greater than or equal to about 80%, or greaterthan or equal to about 90%, or even about 100%.

In an embodiment, the second optical filter layer may transmit the lightin a wavelength region of less than or equal to about 500 nm with atransmittance of, for example, greater than or equal to about 90%,greater than or equal to about 92%, greater than or equal to about 94%,greater than or equal to about 96%, greater than or equal to about 98%,greater than or equal to about 99%, or even about 100%.

The display device may have improved brightness (for example, of greaterthan or equal to about 100 nit (candelas per square meter, cd/m²) and awide viewing angle (for example, of about 160 degrees or greater).

An embodiment provides an electronic device including the quantum dot.The device may include a light emitting diode (LED), an organic lightemitting diode (OLED), a sensor, a solar cell, an imaging sensor, or aliquid crystal display (LCD), but is not limited thereto.

In an embodiment, the electronic device may be an electroluminescentdevice. In the EL device, a light emitting layer including a pluralityof the aforementioned quantum dots may be disposed between an anode anda cathode facing each other.

In an embodiment, the anode, the cathode, or a combination thereof(e.g., disposed on a transparent substrate) may include a metal oxidetransparent electrode (e.g., ITO electrode). The anode, the cathode, ora combination thereof (e.g., disposed on a transparent substrate) mayinclude a metal (Mg, Al, etc.) having a predetermined (e.g., relativelylow) work function. For example,poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate (PEDOT:PSS), ap-type metal oxide,poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB),poly(N-vinylcarbazole) (PVK), or a combination thereof may be disposedbetween the transparent electrode and the light emitting layer, as ahole injection layer, a hole transport layer HTL, or a combinationthereof, respectively. An electron auxiliary layer (e.g., electrontransport layer) may be disposed between the light emitting layer andthe cathode (see FIG. 5).

A device according to an embodiment may have an inverted structure.Herein, a cathode disposed on a transparent substrate may include ametal oxide transparent electrode (e.g., ITO, fluorine doped tin oxide(FTO)) and an anode facing the cathode may include a metal (e.g., Au,Ag, etc.) of a predetermined (e.g., relatively high) work function. Forexample, an n-type metal oxide (ZnO) may be disposed between thetransparent electrode and the light emitting layer as an electronauxiliary layer (e.g., an electron transport layer). MoO₃ or anotherp-type metal oxide may be disposed between the metal anode and the lightemitting layer as a hole auxiliary layer (e.g., a hole injection layer)The TFB, the PVK, or a combination thereof may be disposed between thetransparent electrode and the light emitting layer as a hole transportlayer (HTL). (see FIG. 6).

Hereinafter, embodiments are illustrated in more detail with referenceto examples. However, the present disclosure is not limited thereto.

EXAMPLES Analysis Method 1. Ultraviolet (UV)-Visible Absorption Analysis

An Agilent Cary5000 spectrometer is used to perform a UV spectroscopyanalysis and UV-Visible absorption spectrum is obtained.

2. Photoluminescence Analysis

Photoluminescence Analysis is done using Hitachi F-7000 spectrometer anda photoluminescence spectrum is obtained.

3. Relative Quantum Yield (QY) of the Quantum Dot

For the synthesized quantum dot, a relative PL (photoluminescence) QY(quantum yield) is obtained as below.

QY=QY_(R)*OD_(R)/OD_(sample) *I _(sample) /I _(R)*(n _(sample))²/(n_(R))²

OD: optical density (determined by the absorption intensity in a UV-Visabsorption spectroscopic analysis)

I: Integrated intensity (calculated by the integration of theluminescent peak on a PL spectrum)

n: refractive index of solvent

R: reference dye (e.g., coumarin (green) or rhodamine 6G (red))

Sample: the QD sample as synthesized

4. ICP Analysis

An inductively coupled plasma-atomic emission spectroscopy (ICP-AES)analysis is performed using Shimadzu ICPS-8100.

5. Brightness and Luminous Efficiency of Quantum Dot Polymer Composite

(1) Brightness of the composite is measured as below:

Quantum dot-polymer composite film is inserted between the light guidepanel and an optical film of a 60 inch television (TV) equipped with ablue light emitting diode (LED) having a peak wavelength of 449nanometers (nm). Then, the brightness of the quantum dot-polymercomposite film is measured using a spectro-radiometer (PSI DARSA-5200)placed 45 centimeters in front of the TV when the TV is turned on.

Quantum dot-polymer composites are prepared by separating the quantumdots from a quantum dot dispersion via the non-solvent precipitation andcentrifugation. The separated quantum dots are mixed with a monomer orpolymer (e.g., an acrylic polymer, a thiolene polymer or a mixturethereof) to obtain a mixture, which is then applied on a substrate and abarrier film is covered thereon and a resulting structure is cured.

The obtained composite film is placed on an integrating sphere and anexcitation light having a wavelength of 450 nm is irradiated thereto tomeasure a conversion efficiency of the composite film. Thephotoconversion efficiency is explained above.

6. TEM Analysis

A transmission electron microscopic (TEM) analysis is performed usingTitan ChemiSTEM electron microscope.

Preparation of Core Example 1

Selenium is dispersed in trioctylphosphine (TOP) to obtain a Se/TOPstock solution.

Indium acetate, zinc acetate, and palmitic acid are dissolved in1-octadecene in a 200 milliliter (mL) reaction flask, subjected to avacuum state at 120° C. for one hour. A mole ratio ofindium:zinc:palmitic acid is 1:1:3. The atmosphere in the flask isexchanged with N₂. After the reaction flask is heated to 200° C., atrioctylphosphine (TOP) solution of tris(trimethylsilyl)phosphine(TMS₃P) and the Se/TOP stock solution is quickly injected, and thereaction proceeds at 300° C. for 10 minutes.

The reaction mixture then is rapidly cooled to room temperature andacetone is added thereto to produce nanocrystals, which are thenseparated by centrifugation and dispersed in toluene to obtain a toluenedispersion of the InPZnS cores.

The amount of the selenium is about 0.2 moles per one mole of zinc. Theresults of the TEM analysis confirm that the size of the InPZnS coresthus obtained is about 2.5 nm on average.

For the InPZnS cores, an ICP-AES analysis and a UV-Vis absorptionspectroscopic analysis are conducted and the results are shown in Table1 and FIG. 7.

Comparative Example 1

In a 200 mL reaction flask, indium acetate, zinc acetate, and palmiticacid are dissolved in 1-octadecene and the resulting solution issubjected to vacuum at 120° C. for 10 minutes. A ratio of the indiumwith respect to the palmitic acid is 1:3. The atmosphere in the flask isreplaced with N₂. While the resulting solution is heated to about 200°C., a trioctylphosphine (TOP) solution of tris(trimethylsilyl)phosphine(TMS₃P) is quickly injected.

Then, a temperature is raised to 270° C. and kept for 10 minutes tosynthesize a core. Then, the Se/TOP stock solution is injected theretoand a temperature of the reaction flask is kept at 300° C. for 10minutes to form a ZnSe shell on the synthesized core.

The reaction mixture then is rapidly cooled to room temperature andacetone is added thereto to produce nanocrystals, which are thenseparated by centrifugation and dispersed in toluene.

The amount of the selenium is about 0.2 moles per one mole of zinc. Theresults of the TEM analysis confirm that the size of the core thusobtained is about 2.3 nm on average.

For the InP/ZnSe particles, an ICP-AES analysis and a UV-Vis absorptionspectroscopic analysis are conducted and the results are shown in Table1 and FIG. 7.

TABLE 1 mole ratio P:In Zn:In Se:In In:In Example 1 0.67:1 0.35:1 0.18:11.00:1 Comparative 0.67:1 0.44:1 0.18:1 1.00:1 Example 1

The results of Table 1 and FIG. 7 confirm that the quantum dots preparedin Example 1 and Comparative Example 1 have the similar composition, butin the case of the alloy core of Example 1 has a 1st absorption peakthat is blue-shifted in comparison with that of the core/shell quantumdot of Comparative Example 1.

Alloy Core/Shell Quantum Dot

Example 2

Selenium and sulfur are dispersed in trioctylphosphine (TOP) to obtain aSe/TOP stock solution and a S/TOP stock solution, respectively.

In a 200 mL reaction flask, zinc acetate and oleic acid are dissolved intrioctyl amine and the solution is subjected to vacuum at 120° C. for 10minutes. The atmosphere in the flask is replaced with N₂. While theresulting solution is heated to about 320° C., a toluene dispersion ofthe alloy core prepared in Example 1 is injected thereto and the Se/TOPstock solution and the S/TOP stock solution are injected into thereaction flask. A reaction is carried out to obtain a reaction solutionincluding a particle having a ZnSeS shell disposed on the alloy core.

Then, at the aforementioned reaction temperature, the S/TOP stocksolution is injected to the reaction mixture. A reaction is carried outto obtain a resulting solution including a particle having a ZnS basedshell disposed on the ZnSeS shell.

An excess amount of ethanol is added to the final reaction mixtureincluding the InPZnSe/ZnSeS/ZnS quantum dots, which are thencentrifuged. After centrifugation, the supernatant is discarded, and theprecipitate is dried and dispersed in chloroform to obtain a quantum dotsolution (hereinafter, QD solution).

For the obtained QD solution, an ICP-AES analysis is made and theresults are shown in Table 2. A photoluminescence spectroscopic analysisis made for the QD solution, and the results are shown in Table 3.

Comparative Example 2

A ZnSeS/ZnS shell is formed in the same manner as in Example 2 exceptfor using a core prepared in the same manner of Comparative Example 1.For the obtained QD solution, an ICP-AES analysis is made and theresults are shown in Table 2. A photoluminescence spectroscopic analysisis made for the QD solution, and the results are shown in Table 3.

TABLE 2 mole ratio (ICP data) Sample P:In S:In Zn:In Se:In In:In Example2 0.79:1 16.64:1 38.43:1 14.57:1 1.00:1 Comparative 0.79:1 16.43:138.29:1 14.93:1 1.00:1 Example 2

TABLE 3 Photolumine Full Width scence (PL) at Half Peak MaximumWavelength (FWHM) QY composition (nm) (nm) (%) Comparative InP/ZnSeS/ZnS539 41 66 Example 2 Example 2 InPZnSe/ZnSeS/ZnS 536 41 86

The results of Table 3 confirm that the quantum dots of Example 2 showsignificantly improved QY in comparison with the quantum dots ofComparative Example 2.

Example 3: Quantum Dot Polymer Composite I

A toluene dispersion of the alloy core prepared in Example 1 is added toa monomer/oligomer mixture prepared as below to obtain a composition, 1gram (g) of which is drop casted on a glass substrate:

30 parts by weight of a lauryl methacrylate monomer, 36 parts by weightof a tricyclodecane dimethanol diacrylate monomer, 4 parts by weight ofa trimethylol propane triacrylate monomer, 20 parts by weight of anepoxy diacrylate oligomer (purchased from Sartomer) are mixed to obtaina monomer/oligomer mixture. 1 part by weight of1-hydroxy-cyclohexyl-phenyl-ketone, and 1 part by weight of2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide are added thereto toobtain a final mixture, which is then defoamed under vacuum.

The casted composition is covered with a poly(ethylene terephthalate)(PET) film and is UV-cured with a light intensity of 100 milliwatts persquare centimeter (mW/cm²) for four minutes to produce asemiconductor-polymer composite film. For the obtained film, brightnessis measured and the results are summarized in Table 4.

Comparative Example 3

A quantum dot polymer composite is prepared in the same manner as inExample 3 except for using the core-shell quantum dots prepared inComparative Example 1.

TABLE 4 Film brightness (%) Example 3 53.3 Comparative 54.5 Example 3

The results of Table 4 confirm that the quantum dots of Example 1 mayshow increased brightness and improved chemical stability in a compositefilm.

Example 4: Pattern of a Quantum Dot Polymer Composite

(1) A dispersion of the quantum dots prepared in Example 2 is mixed witha solution of a binder polymer, which is a four membered copolymer ofmethacrylic acid, benzyl methacrylate, hydroxyethyl methacrylate, andstyrene, (acid value: 130 milligrams (mg) per gram of KOH (mg KOH/g),molecular weight: 8,000 grams per mole (g/mol), acrylic acid:benzylmethacrylate:hydroxyethyl methacrylate:styrene (molarratio)=61.5%:12%:16.3%:10.2%) (solvent: propylene glycol monomethylether acetate (PGMEA), a concentration of 30 percent by weight (wt %))to form a quantum dot-binder dispersion.

To the quantum dot-binder dispersion prepared above, a hexaacrylatehaving the following structure (as a photopolymerizable monomer),ethylene glycol di-3-mercaptopropionate (hereinafter, 2T, as amulti-thiol compound), an oxime ester compound (as an initiator), TiO₂as a metal oxide fine particle, and PGMEA (as a solvent) are added toobtain a photosensitive composition.

Based on a total solid content, the prepared composition includes 40 wt% of quantum dots, 12.5 wt % of the binder polymer, 25 wt % of 2T, 12 wt% of the photopolymerizable monomer, 0.5 wt % of the photoinitiator, and10 wt % of the metal oxide fine particle. The total solid content isabout 25%.

(2) Preparation of a Pattern of a Quantum Dot Polymer Composite and aThermal Treatment Thereof

The photosensitive composition obtained as above is spin-coated on aglass substrate at 150 revolutions per minute (rpm) for 5 seconds (s) toprovide a film. The obtained film is pre-baked at 100° C. (PRB). Thepre-baked film is exposed to light (wavelength: 365 nanometers (nm),intensity: 100 millijoules, mJ) under a mask having a predeterminedpattern (e.g., a square dot or stripe pattern) for 1 s (EXP) anddeveloped with a potassium hydroxide aqueous solution (conc.: 0.043%)for 50 seconds to obtain a pattern of a quantum dot polymer composite(thickness: 6 micrometers (μm)).

The obtained pattern is heat-treated at a temperature of 180° C. for 30minutes under a nitrogen atmosphere. (POB)

For the obtained pattern film, a luminous efficiency of a pattern andmaintenance of light emission after FOB (i.e., in comparison with thePRB) are measured and the results are shown in Table 5.

Comparative Example 4

A quantum dot polymer composite pattern is prepared in the same manneras in Example 4 except for using the core-shell quantum dots prepared inComparative Example 2 instead of the quantum dots of Example 2.

TABLE 5 maintenance Conversion of light Efficiency emission of patternafter a heat (%) treatment (%) Example 4 24 89 Comparative 28 95 Example4

The results of Table 5 confirm that the quantum dots of Example 2 havegreatly improved stability in comparison with the quantum dots ofComparative Example 2.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. An electroluminescent device comprising a quantumdot, wherein the quantum dot comprises a quaternary alloy semiconductorcore and does not comprise cadmium, and wherein the quaternary alloysemiconductor core comprises indium, phosphorous, zinc, and selenium,and in the quaternary alloy semiconductor core, a ratio of the zinc withrespect to the indium is less than or equal to about 0.5:1 and in thecore, a ratio of selenium with respect to zinc is less than or equal toabout 0.6:1.
 2. The electroluminescent device of claim 1, wherein in thequaternary alloy semiconductor core, the ratio of zinc with respect toindium is greater than or equal to about 0.29 and less than or equal toabout 0.45:1 and in the quaternary alloy semiconductor core, and theratio of selenium with respect to zinc is greater than or equal to about0.1 and less than or equal to about 0.51:1.
 3. The electroluminescentdevice of claim 1, wherein the quaternary alloy semiconductor corecomprises a homogeneous alloy.
 4. The electroluminescent device of claim1, wherein in the quaternary alloy semiconductor core, a mole ratio of atotal sum of the zinc and the selenium with respect to a total sum theindium and the phosphorous is greater than or equal to about 0.2:1 andless than or equal to about 0.65:1.
 5. The electroluminescent device ofclaim 1, wherein the quantum dot has a semiconductor nanocrystal shellon the quaternary alloy semiconductor core and the semiconductornanocrystal shell comprises zinc, selenium, and sulfur.
 6. Theelectroluminescent device of claim 5, wherein the semiconductornanocrystal shell comprises a first layer disposed on the quaternaryalloy semiconductor core and a second layer disposed on the first layer,the first layer comprising a first semiconductor nanocrystal, and thesecond layer comprising a second semiconductor nanocrystal having acomposition different from a composition of the first semiconductornanocrystal.
 7. The electroluminescent device of claim 6, wherein anenergy bandgap of the second semiconductor nanocrystal is greater thanor equal to an energy bandgap of the first semiconductor nanocrystal, orwherein the first semiconductor nanocrystal comprises zinc, selenium,and optionally sulfur, and the second semiconductor nanocrystalcomprises zinc and sulfur and does not comprise selenium, or wherein thesecond layer is an outermost layer of the quantum dot.
 8. Theelectroluminescent device of claim 1, wherein in the quantum dot, a moleratio of zinc with respect to indium is greater than or equal to about25 and less than or equal to about
 45. 9. The electroluminescent deviceof claim 1, wherein in the quantum dot, a mole ratio of selenium withrespect to indium is greater than or equal to about 5:1 and less than orequal to about 20:1.
 10. The electroluminescent device of claim 1,wherein the quantum dot further comprises sulfur and in the quantum dot,a mole ratio of sulfur with respect to indium is greater than or equalto about 10:1 and less than or equal to about 25:1.
 11. Theelectroluminescent device of claim 1, wherein the quantum dot furthercomprises sulfur and in the quantum dot, a mole ratio of sulfur withrespect to selenium is greater than or equal to about 0.8:1 and lessthan or equal to about 1.5:1.
 12. The electroluminescent device of claim1, wherein the electroluminescent device comprises an anode and acathode facing each other and a light emitting layer between the anodeand the cathode, and the light emitting layer comprises the quantum dot.13. The electroluminescent device of claim 12, wherein theelectroluminescent device further comprises a hole auxiliary layerbetween the anode and the light emitting layer, an electron auxiliarylayer between the cathode and the light emitting layer, or a holeauxiliary layer between the anode and the light emitting layer and anelectron auxiliary layer between the cathode and the light emittinglayer.
 14. The electroluminescent device of claim 1, wherein a maximumphotoluminescence peak of the quantum dot is in a range of from about500 nanometers to about 580 nanometers.
 15. The electroluminescentdevice of claim 1, wherein a maximum photoluminescence peak of thequantum dot has a full width at half maximum of less than or equal toabout 45 nanometers.
 16. The quantum dot of claim 1, wherein a quantumefficiency of the quantum dots is greater than or equal to about 70%.17. A method of producing a quantum dot included in anelectroluminescent device of claim 1, which comprises: preparing aquaternary alloy semiconductor core by conducting a reaction among anindium precursor, a zinc precursor, a selenium precursor, and aphosphorous precursor in an organic solvent in the presence of anorganic ligand to form the quaternary alloy semiconductor core, whereinthe selenium precursor comprises a selenium-trioctyl phosphine, aselenium-tributyl phosphine, a selenium-triphenyl phosphine, or acombination thereof.
 18. The method of claim 17, wherein the reaction iscarried out a to temperature of greater than or equal to about 290° C.and the method further comprises mixing the indium precursor and thezinc precursor in the organic solvent in the presence of the organicligand to obtain a mixture; heating the mixture at a temperature ofabout 150° C. and 220° C. to obtain a heated mixture; and adding theselenium precursor and the phosphorous precursor to the heated mixture.